I'm trying to find what FAIR pricing would be for a registered full auto AR... Or what a registered autosear runs these days.  I know it'll be ungodly expensive, but I'm considering going class III.  Anyone know?  Sportsmans Supply, you probably know about about this stuff... I don't mind paying through the nose, as long as it's market price, I just don't want to get taken.

go to subguns.com and look at the NFA board.

You can get a Registered Receiver for around 4k.  If you want Colt, its around 5k+  

I got my EA lower for 4200 last year.

7 is right; go to the subguns board and watch the ads there for at least a few days.  You'll get a good idea of market price for various registered AR15/M16's.

The NFA market is soft right now, so its a good time to buy.  Generally you should expect to pay:

between $4-5k for a non-Colt AR15 converted to F/A.
About $4500-5500 for a converted Colt AR15
$5500-7000 for a factory Colt M16A1, 613, etc.
$7500-8500 for a factory Colt M16A2, maybe more

A registered DIAS will run about $4k
A registered link will be about $2500

unless ...

You are buying a full-auto Mac .. in range within $1000

Forgive my ignorance, but what's a registered link?
Does purchasing the registered sear allow me to convert a post ban into a legal full auto, like the guy at my local shop said?  
And if so, how easy is that to do?

A link (aka "lightning link" or auto-disconnector) and a DIAS (drop in auto sear) are conversion parts.  Neither of these parts require modification to the lower.  In fact, you cannot do anything more than minor fitting adjustments to the receiver of the host gun with these parts; no milling, no drilling.  These parts are completely "drop-in" units.  The DIAS acts exactly like the pinned in type of autosear found in a standard M16.  A DIAS only needs the installation M16 fire control parts in the host AR15 to work with it.  The lightning link works differently - by pulling the disconnector as the bolt goes into battery, thus tripping off another round.  No M16 parts are needed with a link - it works off of the standard AR15 parts.  Of the two, the DIAS is by far more sturdy and reliable.  The trip lever on the link will occasionaly bend, and you'll have to poiund it flat for it to work again - not a big deal, just annoying.

Additionally (per my understanding) a link conversion is either auto or safe while a DIAS conversion is select fire (auto, semi, and safe). Furthermore any post-ban converted via registered DIAS or link can have all the pre-ban evil features as well as barrel lengths less than 16" since the installation of the link/DIAS makes the whole rifle a machine gun and not an "assault weapon" under the law. Of course, a true assault weapon is already full auto while the govt definition for an AW means flash hiders, bayonet lugs and folding/telescoping stocks.
I plan to go the RDIAS route myself...thanks to shaggy... IT'S ALL YOUR FAULT!!!      THANKS!!!!

a lighting link can be select fire just takes specialy modded m16 parts or so i heard