2002 Grand Cherokee 60k miles with no reverse

Hi. About a monthago my Jeep Grand Cherokee lost it's reverse. I was in a parking lot and put the jeep in reverse whe I hard a loud pop and it wouldn't move. I took it to an overzealous transmission center and they told me I needed a rebuild. Is this true since it goes forward perfectly fine? How much am I looking to spend on a repair? My mechanic doesn't want to touch it as it's not his specialty. Here's the kicker, about a week before the tranny started acting up I had to replace the fan regulator and the engine light came on when I removed a cable. There were two codes that registered on the diagnostic, 1 was the regulator and I didn't write down the other one and the memory was erased.
Thanks