First off, use the search feature to pull threads about transmissions. There is enough info to keep you busy for many hours.
As a rough estimate a rebuilt trans for towing duty with a good converter will start about $3000 and go up from there depending on how trick you want it.
Take a look for threads comparing multi-disk converters to single disk converters. There is a wealth of info on the threads but you will have to dig to find it.
When you feel you know enough to know what questions to ask start calling the vendors and get their advice, recomendations, and price. If you want quality and reliability its going to cost $$$. Don't be fooled by the cheaper adds and shops that promise a bullet proof rebuild for much less than $3k. You won't be happy and will have to do it over.
There are several major vendors, DTT, ATS, Goerends, BD, Suncoast, and they all have web sites with varying amounts of info. Talking to the right people at these places will get you plenty of choices and ideas.
Good luck.