average garage, 22×22, no drywall existing, figuring hardy siding replacing door. ceiling joists are probably 24 in. on center and need to be 16. assuming your existing a/c unit is big enough to handle the extra space, i would say realistic ballpark is 8700- 9500. small-town USA, less 1000.

Careful…… conversion of the garage is usually frowned on by the City or County unless you provide other off street parking.
Think you can get away with it? think again there is always a nosy neighbor that notices “their garage door is never open” I did some floor repair for a guy that did one several years ago and sure enough the neighbor turned him in. He waited till it was all done and then turned him in. Good for him because that guy screwed me out of $200.00.
I’m not saying you cant do it but its best if you check first. The cost someone else gave was about right in the $5000.00 range

Depending on where you live; 300.00 per sqare foot seems to be the going rate in San Francisco.

maybe less than 5k thats not that much to it because you already have th main structure its just putting it together and sub it out by diff ppl its alot cheaper good luck!!!!