Transmission control module....?

I took my 95 Eagle Vision TSI to a transmission shop have my fluid change when he told me there is a problem with my Transmission Control Module (TCM). Therefore he was not able to change the fluid and he wanted to charge me 785.00 buck to diagnose the problem with the control module. That is way too much money but he said its better than replacing the transmission. I wanna know would it be cheaper for me to buy a new TCM rather than spending the 785.00 at the shop just so they can tell me whats wrong with it. I looked up how much a new one costs and its only 145.00 bucks. What should I do?