Generally, 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.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.