I contracted out a 980 sq foot shop building which included an 8 x 10 bathroom for $28 per sq foot walled in, wired, insulated and sealed. It has 1560 sq feet under roof, but only the 980 is on slab. That would make a nice 1 bedroom or even 2 bedroom house. That price does not include the septic system that I had put in for $6500 or any water well. The kitchen cabinets and appliances are probably the most expensive part of a house this size, but if you already have a range / oven /refrigerator that would take away a big expense. The cabinets would still be a strain to put in enough to be practical and not blow your budget. I suppose that if you did some of the work yourself and didnt have to put in a well you could build a small house of 1200-1500 sq ft for $45000, but you would have to go with the cheapest materials that you could get and so a lot of the work yourself. Even if you went the $.99 cent floor tile thru out the house, most till layers charge at least $2 per sq. foot to lay them, but it isnt hard to do it yourself with some basic tools and a $100 diamond blade wet tile saw if you have a strong back and good knees. Most of the work you can do yourself and then pay a licensed person to inspect it and sign off. A lot depends on where you live and the local officials. For instance, get an electrician to design your circuits and wire schedule, then you can pull the wire and get the electrician to hook it up and save a lot of money You can get a plumber to lay out the ditches, but you dig them and save some money. If you have any civil skills, you could even put in your concrete slab by soliciting some labor by the hour to place the concrete. Dry wall professionals will often do a job on the weekends cheaper than a contractor, you just have to watch out for lack of insurance issues should some one get hurt.