Sandblasting inner quarter panels and side pillars.

I have my 68 mustang about stripped down to go to get sandblasted and if you'll see in the pictures below the inner upper quarter panel right after the rear window is rusted pretty good on both sides. Will the blasters be able to get in there and remove all that or will removing the quarter panels have to happen?

I'm just having the main shell, minus doors and floor pans ( they are getting replaced ) no hood or trunk lid done. Just the rest if the inside and outside blasted and was quote 700 bucks and seems a little high to me...that about right?

Inside quarter panels look fine ( from what I can see with the rear aprons removed ) it's the area above in the pictures that needs blasting/rust remove. I just don't have a clue how to get in there and do it. I have no problems doing some manual labor rust removing just want to avoid taking the quarter panels off. That's a little out of my league of skill. Also I could not find any replacement sheet metal for them incase that inner frame needs replacing.
I know you can replace the roof with a new unit but it does not include the area between the quarter panel and the rood ( whatever its called ). I guess I might be stuck removing quarters to get in there all the way?