I know it depends...but say we have a pretty standard single-family, 2100 sqft, new "split" system install 4ton , and attic condenser/coils/furnace
Anyone had one put in over the last year or two?

5k to 20k depending on what level of quality and work you want done.

@buckshot_jim - thats almost the exact same amount I got hit with.  
Thought it seemed ridicously high.  Then again, so are truck prices.
Price includes 10yrs parts & labor warranty.  

Check ACWholesalers.com

Several years ago I bought a 4 ton 19 SEER system from them for under $3k delivered and a guy I know installed it for $600.00.

It's been really trouble free...and for what some of these clowns charge - I can replace it all with a brand new package 3+ times.

Whoah!  For what I got, I see roughly the equivilant for much less
https://www.acwholesalers.com/cooling/split-system-air-conditioners.html

It depends on what you got.  That link is for builder grade stuff.  Not saying it’s bad but it is built to a price point.  It can work but how well and for how long is the real question.    AC equipments can be the same as cars.  You can purchase the cheapest Kia car made or the most expensive Mercedes.  They are both cars and for the most part get you from point A to point B.  One of them would be nicer to drive cross county and one of them will not.

You have to determine comfort and efficiency on your purchase.  I spent closer to 12k for my last unit because I have seen and lived in a house with a cheap and crappy  setup.  I prefer comfort over saying look at how little I spent.  Also the person doing the install is more important then the equipment.  Crappy install with over or under sized nice equipment is waist of money vs a good install and properly sized cheap equipment.  

One way to determine who not to hire is exclude anyone that goes off your sq ft only and does not do any type of load calculations on how your home is built and where it’s located.  There is no such thing as 1 ton equals X sq ft of living space or “rule of thumb”

The installer is coming out Tuesday to replace my 18 year old heat pump.

4 bedrooms, 2040 square ft. $5282 flat price.  Rheem system.

I just had some replaced a couple months ago. ~34k all in for 2 x 3 ton units, uvc lights for 3 units, new duct work, a couple solar attic fans and tune up of existing 4 ton unit. The 2 x 3 ton new units i put in were electric carrier 24 seer variable speed heat pumps.

Get at least 5 bids. Some go for the "rip your head off" pricing, or nothing at all. What is your AO? Make sure your insulation is gtg.

I just paid $10200 for a 16 seer 3.5 ton unit. People on here tell me I overpaid though.

ETA: Its all lennox stuff.

NMG

Paid 17k for a 4 ton unit with new ducting in a 2500 sq ft house in west Texas a year  ago

400 sqft = 1 ton of AC

$2,500 per ton

This rule of thumb gets you close to what you should expect.

And this is why anyone that uses a “rule of thumb” when they come to your house for a estimate should never be used.  

That “rule of thumb” would have had me install a system twice the size needed for a house in west Texas.   It would have been more then 3 times what was needed for another house because of the construction type.  It would have caused nothing but short cycles and the indoors would have been humid as hell.

Same,  except we did a 2-zone setup (we had to replace everything due to the previous owner having a poorly-maintained humidifier on the old system).
HeatPump, 2-zones, and a 2-stage blower.  Edit: home is just a little larger than Jim’s.

Was $16K to replace the indoor and outdoor units for my downstairs less than a month ago.