Is there a way to un warp a pan bottom?
A technique that works for some car dents is to apply dry ice to the warp and this may cause sufficient contraction from the cold the remove a warp. I think this is a low probability of success...but it might be cheap enough to try.

Second, you might consult a local blacksmith (yep, they're still out there) who has the equipment to heat the metal to where he can 'flatten' it for you. I suspect this would cost more than replacing it.