Blasting does actually take a good bit of skill, especially when you deal with the high volume/pressure air systems they use. It can be very easy to warp a panel. With that said, though, there is no way in he11 the cost should ever come close to $6K, let alone half that. My car was blasted (nothing underneath) for I believe $750 last year. It's not uncommon for them to run into additional costs for time and material when they do the undercoating (I watched them spend a couple hours blasting just one wheel well on a mustang while I was dropping my car off), but again, and kind of additional charges should be worked out before that particular work is done. I hope you have luck with the lawyer, because unfortunately you're going to need it without anything in writing. If you take him to small claims, don't go to Judge Judy.