Car will not Move in reverse, car moves in all other gears

I was driving from work two weeks ago, I got home park the car after twenty minutes I went back outside to got to the store, start the car put it in reverse and it would not move, all the gears work except reverse gear. I have no problem from first gear to fourth gear, when I put the car in reverse it will role back very slow, the owner that I got the car told me he paid $1,800.00 to rebuild the transmission. Do not have the money to get another car or do a rebuild. My question is, would it be a good idea to get a used transmission? I checked the cost for a used and can get one for $250.00, but before I get a used one is there something that would take out my reverse gear?

Thank you in advance.