The tools to rebuild most automatics are expensive these days. What used to be $100-$150 for tools, I think will run more like $300 or more for sure. So to attempt a rebuild yourself, you need to be prepared for the cost of several special tools.
If there is no extensive internal damage, the parts besides the clutches/seals, then a rebuild is not a huge deal for anyone mechanically skilled. It is tedious and takes good patience to be sure that nothing is misplaced, mixed up, and all is put back exactly as intended. A basic $15 manual can cover almost everything you would have to know, and that is the absolute must have first thing to buy, and read.
Parts can be as little as $150, but a torque converter and replacing all solenoids, accumulators, and other broken or damaged parts, are most of a rebuild cost, not counting labor. Shops make their profit on the R&R of the trans, not the actual rebuild. Their high cost is partly to cover come backs, which can be many and expensive to them.
Be sure to install a new external filter in the cooler lines. That can be a simple inline filter placed in the return line(not the output line).