Okay, I have the bug to build one now so, I'm going to do a "Budget Build."
My goal is a sub $2000 $1500 build, including tax stamp and engraving, that looks like a MK18 Mod0 without the serious sticker shock-the wife is going to kill me money involved.
I will post pictures of the before and after once I get my tax stamp.
Project was started on 9-15 when I picked up my donor rifle at my LGS. All upgrades for the build commenced after that and are listed as being completed or in hand for the build.

This is where I am at now:

Platform: Bushmaster XM15-E2S 16" M4 profile barrel (flat top w/ carry handle)l:  $495.00
 (Gunbroker buy out of a Colorado pawn shop. Was missing the pin for the gas tube causing it to slide out of position causing functioning issues. Otherwise a really nice rifle.)
New Gas Tube and Pin: $12.00 (Ebay)
Flash Hider: Doublestar Eliminator: $28.00 (Midway) I like it and it's cheaper than a KAC piece.
New Matech BUIS: $35.00 (Ebay; new in packaging with instructions)
New KAC RIS: $112.00 (Ebay; new in the boss with all accessories.Plastic rail cover case has spotting from some type of oil that was on it. Everything else is mint)
Tango Down Battle Grip, Black: $29.00 (Ebay, used mint condition)
Milspec Style Buffer Tube: $14.00 (Ebay. Really nice overall. You can see some slight surface imperfections on the outside; stock covers those. Stock functions and locks up great with no unnecessary play. Overall, nice for the price.)
B5 Systems Enhanced SOPMOD Stock, Black: $79.00 (Ebay, Brand F'n New)

Running Total: $804.00

Ambi-Safety added at $19.00. I am not counting this in the price. It's a lefty friendly feature for me.
Also, LN M4 double heat shield handguards from a LGS, $5. They were temporary as I hate the standard carbine handguards.

Haven't decided on doing a new /used complete upper, new barrel & bolt, or barrel chop & threading yet. So that part is up in the air.
Leaning towards a 10.5" upper from jwill242004 at ANDROCORPIND.com in the EE. They have'm with M4 handguards for about $385 on Gunbroker.  Yes, not the 10.3" barrel length, but close enough for the budget builder.
Optics; looking at the Aimpoint PRO, M2, or M3. Shooting for a nice used but not abused piece for a good price. That will depend on what's available when I get to that stage (probably next week or the week after.)
Weaponn Light will either be a Surefire M962 or a M952V-BK (Black).
No laser or anything like that. I personally don't need it. Unless somebody wants to donate a LDI DBAL-D2 in black for my build (Christmas isn't that far off.)

I will update my budget build as I progress.

Any thoughts or contributing ideas on the project are gladly welcome.
Hopefully others on a budget will see that it can be done with patience, saving, and selling lots of crap you don't need.

Glad to see you support anti gun, anti second amendment FleaBay.

Have you got your tax stamp yet or are you going the sig brace route?

There is a MK18 thread already just for this very thing.

Cheapest to cut the barrel you have now. I would have it done at Rainier Arms and tell them what ammo you use and whether you will ever use a can.

Also, the Daniel defense flash suppressor is more like a KAC than anything but a KAC, and the price is good.

You could buy this from psa and sell the upper and have an Aimpoint PRO for $300.

Eta: free shipping on uppers this weekend

For a good budget MK18, get a PSA put together for around $550.

I was in there when I posted this. Must have hit new topic or something to get in the general area.

I buy and sell all kinds of stuff on ebay, so I can't complain.
Hell you can find barrels, bolt carriers, and other stuff on there.
No firearms, which sucks. But I'm not going to pass sourcing items on ebay when deals can be found.

No stamp yet. I should be eFiling that in within the next few weeks. I need to check out the thread on eFiling and BATFE site to see what is inolved.
The last stamp I did was about two years ago via the mail.

Thanks'.
I'll check these out. No cans in Minnesota unfortunately.

Thank's for the lead. I'll check it out.

Or keep the upper and send the barrel to Adco and have it cut down to 10.2".

 

Chopping the barrel is the route I will most likely go. Either Adco or Rainier Arms.
I will need to have the gas port resized. Bushy's have a 0.0625" gas port.
I take it I need to run a 0.070" port for M855 and M193 or any of the other 55gr and 62gr ammo I plan on using?

Oops.

Update:  Added a Aimpoint PRO to the list.

I plan on removing the QRP2 base and replacing it with a QRP or QRP3 from Aimpoint.  

This is where I am at now:

Platform: Bushmaster XM15-E2S 16" M4 profile barrel (flat top w/ carry handle)l: $495.00
(Gunbroker buy out of a Colorado pawn shop. Was missing the pin for the gas tube causing it to slide out of position causing functioning issues. Otherwise a really nice rifle.)
New Gas Tube and Pin: $12.00 (Ebay)
Flash Hider: Doublestar Eliminator: $28.00 (Midway) I like it and it's cheaper than a KAC piece.
New Matech BUIS: $35.00 (Ebay; new in packaging with instructions)
New KAC RIS: $112.00 (Ebay; new in the boss with all accessories.Plastic rail cover case has spotting from some type of oil that was on it. Everything else is mint)
Tango Down Battle Grip, Black: $29.00 (Ebay, used mint condition)
Milspec Style Buffer Tube: $14.00 (Ebay. Really nice overall. You can see some slight surface imperfections on the outside; stock covers those. Stock functions and locks up great with no unnecessary play. Overall, nice for the price.)
B5 Systems Enhanced SOPMOD Stock, Black: $79.00 (Ebay, Brand F'n New)
Aimpoint PRO:  $362.00 (Ebay, like new safe queen optic)

Running Total: $1166.00

No offense but how is it hard to do this under $2k?
Someone just posted factory MK18s for $1200. Stamp makes $1400 and optic, brand new, makes $1800.
I realize you're after a mod0 but still...
PSA complete 10.5 for like $700 and the kac and B5 you snagged makes $900

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None taken.
Starting with a used AR is just one option. So, I figured I would just see what the cost would be.
The $2000 was a guess on my part before I even started, so I stuck to it.  I figure I should be under $1500.

Crappy picture of the Bushmaster XM15-E2S purchased for this project.
It came in the Allen case with a pocket full of crap. Well mostly crap. There was also a really nice Surefire Z2 flashlight. That's being sold to offset the cost of the rifle.

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New Update: This is where I am at now:

Found a P&S Products produced RIS; bringing the cost down more. I'll save the KAC set for another build.
Also picked up a early style Aimpoint QRP mount with spacer. I'll sell the QRP2 with a bunch of other stuff from this project to offset the build cost.

All that is left is the Tax Stamp, barrel chop, and Surefire light.
I'm going to finish up my BATFE eFile this weekend and get it sent off.

Platform: Bushmaster XM15-E2S 16" M4 profile barrel (flat top w/ carry handle): $495.00
(Gunbroker buy out of a Colorado pawn shop. Was missing the pin for the gas tube causing it to slide out of position causing functioning issues. Otherwise a really nice rifle.)
New Gas Tube and Pin: $12.00 (Ebay)
Flash Hider: Doublestar Eliminator: $28.00 (Midway) I like it and it's cheaper than a KAC piece.
New Matech BUIS: $35.00 (Ebay; new in packaging with instructions)
New P&S Products RIS: $32.00 (Ebay; new in the plastic packaging. Plastic rail covers were separate.)
Tango Down Battle Grip, Black: $29.00 (Ebay, used mint condition)
Milspec Style Buffer Tube: $14.00 (Ebay. Really nice overall. You can see some slight surface imperfections on the outside; stock covers those. Stock functions and locks up great with no unnecessary play. Overall, nice for the price.)
B5 Systems Enhanced SOPMOD Stock, Black: $79.00 (Ebay, Brand F'n New)
Aimpoint PRO: $362.00 (Ebay, like new safe queen optic)
Used Aimpoint QRP (early style) w/spacer: $60.00 (Ebay, really nice condition)

Running Total: $1146.00

Minus Items Sold from build:  $182.00

Total $964.00

MG Ebay, Ebay, Ebay oh theres Midway

You can get QRP mounts all day in the EE around $40-$50 and aimpoints for $350.

If your trying to be cheap check out the EE.  100x better than flea bay.

Project update with a few photos.

Next step: stamp and barrel chop. Submitting the eFile on Monday. Scanning a trust page by page sucks

Last photo is of the Doublestar Eliminator flash hider. Similar to the Micor series but a lot cheaper.

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eForm submitted today. Hopefully a quick turn around like others.
Decided on Adco for the barrel chop to 10.3"

Current Cost Update: Tax Stamp Added.

Platform: Bushmaster XM15-E2S 16" M4 profile barrel (flat top w/ carry handle): $495.00
(Gunbroker buy out of a Colorado pawn shop. Was missing the pin for the gas tube causing it to slide out of position causing functioning issues. Otherwise a really nice rifle.)
New Gas Tube and Pin: $12.00 (Ebay)
Flash Hider: Doublestar Eliminator: $28.00 (Midway) I like it and it's cheaper than a KAC piece.
New Matech BUIS: $35.00 (Ebay; new in packaging with instructions)
New P&S Products RIS: $32.00 (Ebay; new in the plastic packaging. Plastic rail covers were separate.)
Tango Down Battle Grip, Black: $29.00 (Ebay, used mint condition)
Milspec Style Buffer Tube: $14.00 (Ebay. Really nice overall. You can see some slight surface imperfections on the outside; stock covers those. Stock functions and locks up great with no unnecessary play. Overall, nice for the price.)
B5 Systems Enhanced SOPMOD Stock, Black: $79.00 (Ebay, Brand F'n New)
Aimpoint PRO: $362.00 (Ebay, like new safe queen optic)
Used Aimpoint QRP (early style) w/spacer: $60.00 (Ebay, really nice condition)

Running Total: $1146.00

Minus Items Sold from build: $182.00

Rifle Total: $964.00
Tax Stamp: $200.00
Total $1164.00

Done, kinda sorta.
Stamp approved on the 13th (35 days).
I purchased an upper (from Jason in the EE- jwill242004) for another MK18 build, but decided I like it so much that I am going to sell the Bushmaster upper assy. and buy another one.
So all in I'll be at about $1204 for this build.
My next one will be on a Aero Precision lower.
Not the best photo, I'll try to get a better one later.

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EE is your friend, i found lots of good deals on there but you have to be patient.

I built my mk18 over the course of like 3-4 months and built it for probably close to 50% of what it would have cost to buy one directly from DD, but i was in no hurry as i was waiting on my Form 1 approval so i had time to kill.

Yeah, it can be.
I have the original Bushmaster upper and a stock listed to fund another 10.5" upper.
Fingers crossed for a sale.

I love mine, this is the $350 PSA upper

Nice.
Sucks I live in a non-suppressor state.