Denny,
I feel for you. I just took two front fenders, the radiator support and 3 small peices into the only place in my area that can blast sheetmetal without ruining it. Their price is $125.00 an hour. They estimate by the square foot.
My price for this work is $448.00. That sounds like a lot compared to a couple hundred bucks for equipment, but this place blasts the peice, repairs any splits in the metal and epoxy primes the peices so they don't rust afterwards.
The big question for me is whether or not to have my box cleaned up. I know it has some rust issues in a couple of spots and the front panel is pretty well beat out of shape. By the time I get it blasted and repaired, I can probably buy a complete new box. I think I have seen the complete box for around $1600.00