Built our own this year. Room size is 18' x 18'. Not sure of the cost, but I think it was around $1500. We put it in a corner of our barn, so that was two walls. I found 1.5" sheets of insulation cheap, a guy was stripping a roof off of a warehouse. Wood frame/siding was purchased locally. Finished the concrete ourselves. But a new/previously owned a/c on Craigslist, used a Cool Bot. I imagine the cost would have been around $5000 if you had to go and purchase all of the materials new, plus more if you can't do the work yourself.