under existing houses. We were going to add onto our house and looked into doing this. We are on a slope and have 5.5 ft clearance under the house on one side down to two feet on the other. The cost was about $30 more per square foot, around $140 per square foot total. Since a normal addition was $110 per sq ft we just added onto the back of the house with a daylight basement addition. Now that it's done, we are very happy to have the extra space.

I would suggest calling a contractor and they might know someone.