Estimate to rebuild transmission

We don't get involved with costs here because there's way too many variables. You didn't even list which transmission you have. This is a question for the people at a transmission specialty shop. GM transmissions require a number of specialty tools including cones to prevent damaging rubber lip seals as the parts are assembled. Most tranny shops will have those tools and they will have shift kits in stock or they'll know where to get quality parts from.

Today it is common to have to spend $3000.00 to $4000.00 to rebuild a complicated computer-controlled transmission. Yours should cost considerably less than that, but it also depends on whether any internal parts other than the clutch discs and seals need to be replaced.