You need to cut the gasket in order to pull the rear window. So re using the gasket is just not possible.
Body shop labor rates in my area range from $65-$100 an hour. Since they need to pull some interior panals to disconnect the heater connections, and remove that pita trim, I'd figure 3-4 hours labor for any shop.
Rust is another tricky area, any good body shop will want to cut it out and weld in new metal. The shop I took it do does awsome work and flat out refused to do it any other way. They are a very high quality resto shop that doesn't mess around or put their name on anything sub par.
The grinding it down and painting it just buys you time. Since I did this job last year I noticed rust poping up again.
So this year when I paint my car I'll pull the rear window again and see what I find.
One option I am considering is cutting that sill section out of another car and welding it into mine. I am pissed because my 420 parts car I sent out to the junker was rust free under the window. I should have cut it out I wasn't thinking!!
