I have no idea how much it would cost. They charge by the square ft and it also changes according to how tight the space is, ease of access and what's under there. Doing it yourself would probably save you a ton. But the key is getting everything sealed good at your seems, and running the vapor barrier up the walls and foundation supports. Sealing off the vents on the sides and using a foam block for insulation, then the space becomes conditioned and will only be about 2-3* different from the rest of the house, eliminating the chance of mold and being much more efficient than traditional insulation.
