The car still runs fine for now? So, is the tranny slipping?
I'd replace the transmission, ideally myself to make the repair cheaper than the car's worth. If you have a handy friend/relative and you can survive a week without a car, it's doable to do this yourself but it takes TIME without the experience and resources of a shop.
Even if you pay them, I'd still keep the car. Cars in $2k price range are their own time bombs.