So for reference here is my current 30'x40' build (1200 sq ft). I am located in Texas.
- 30'x40' Concrete slab, with rebar, vapor barrier, and footings is just under $10K. This is a good price for this area, and the company is reputable.
- 30'x40'x12' standard metal building from Mueller out the door is $8100 (delivered). I plan on erecting this myself with help from friends.
- I am budgeting $3K for spray in foam which is probably higher than what it will cost. I plan on contracting that out.
- I am budgeting another $4k for items like floor coating, lighting, and electrical. I will be doing that myself as well.
- I'll be buying the garage door online and DIY installing it. I have budgeted another $2K for that.
All of the DIY stuff will be done slowly at a very leisurely pace due to some health issues that keep me from pulling 12 hour heavy work days like I could in my 20s

.
So:
$10K + $8.1K + $3K + $4K + $2K = $27,100 / 1200 sq ft = about $23 sq. ft.
If you are willing to do some of the work yourself you can save a lot of money, and some of the jobs really are not too difficult:
- Floor finishing is a good example. My wife and I saved thousands of dollars DIYing the stained concrete floor when we built our house. We had never done it before, it turned out great, and still looks great 14 years later. It only took three days start to finish. We watched youtube videos, did our homework, and asked the staining materials supplier a few questions.
- Electrical work. Find an electrician that is willing to work with you. When I built my last garage (stick frame) I ran all of the wiring to the garage breaker box and installed all of the plugs, switches, and lighting. I had never done a job that large before but again I just did my homework. My electrician checked out my work when I was finished to be sure it was safe and met code. He then ran the main cable from the garage breaker box to the main breaker box.
EDIT: Whoops I knew I was forgetting something! I'll be buying a 10'x10' double steel insulated door as well. That adds another $2K. Above math corrected accordingly.