Transmission advice please

I have a 1966 Mustang 289 with an automatic transmission in it. It also does not have any exhaust other than the stock manifolds. I found out the other day that it wouldn't shift out of first gear. The transmission came from a 1965 donor car, so I have no idea what could be wrong with it. It does appear, however, to have a new pan on the bottom of it. It leaks transmission fluid like crazy. Now, here is my predicament. Do I get the auto tranny fixed or should i just convert it to a manual? I would rather have a manual, but cash is a concern right now. What should I do, and what am I looking at price-wise to do either of these?
Any comments are greatly appreciated!!!