Agree with the others. I had ZERO experience peering into a transmission of any sort, and with a little help from Hotrod Lincoln and a few others here, I rebuilt it AND the Borg Warner overdrive by myself. I did a thread on it in the Driveline forum, if you want to follow a novice through a learning curve.
Do it yourself and you'll see that they are really very simple (though I did not believe that could be true until I dived in). Then sell your services to that shop.
Parts are both plentiful and reasonable. Go for it.
jim