Our price and cost estimates for a prefab ADU from Oasys range from $290 - $393+ per square foot. These estimates are all inclusive, meaning that the cost of the home, labor, and site work are included. This cost estimate is based on the turn-key cost of a prefab ADU from Oasys. They are transparent about project costs and list turn-key project costs on their website. The cost of land and any home upgrades are not included in this estimate. It is worth noting that Oasys offers end-to-end building services. Below, you can find a table of our cost estimates for a finished house from Oasys.