MotorGround >> 318/360 heads rebuilt worth what?

I want to sell a pair of heads and I don't know how much I should ask for them. They are from the mid 70s, Dodge small valve 318/360 heads, completely rebuilt by a machine shop. All the valves were removed and either recut or replaced. The head was electroflux for cracks. The heads have about 10 miles on them before I junked the vehicle. They've been sitting in my garage for years. They aren't rusty or anything. I was going to post them on Craigs List. How much should I ask for them? I'll even offer a money back guarantee if any of the valves are leaking. I can do this because I know they won't come back. And I'll put it in writing.