For example, a $5,000 well will cost $1 per square foot on a 5,000 s.f. house and $2 a s.f. on a 2,500 s.f. house. Since houses with low square footage of finished space still tend to have garages, porches, and all the other site costs, the cost per square foot tends to be higher.enerally, turnkey costs will start at around $70 a square foot for a starter home in ideal conditions. An average level of finish will be more like $90-100. At $110-120 we are building a custom finish.