Rebuild it yourself. If you rebuilt an engine you can do an trans. Just use the chassis manual with the exploded view diagrams. I bought a seal and gasket kit for my 727 it was 70 dollars, and I went over it myself.
Don't ever forget to install C clips. I Had a bad experience once. U joint slid all the way to one side of the rear yoke while doing 80k, and it gave my 360 a death shake.