The Tremec kits are expensive. You have to email classicchevy5speed for a price quote, but this place offers a complete kit for a 55-57 chevy car, which should be somewhat similar, and it comes in at $3,200.
http://www.classicchevy.com/product....9&dept_id=1857
If you want to use a 700R behind a motor with power you're going to want one that was built to handle it, and don't forget about kits for lock up and to make sure it shifts right (like the bowtie overdrives lock up kits and TV made EZ kits.) That could get pretty expensive.
I have no idea how much a M21 or 22 goes for, so what do you consider cheap?