I agree, that's crazy high to replace a pinion bearing, all the more so if you pull it and the mechanic can do the work on his bench. That kind of money should get you a good limited-slip pumpkin ready to bolt in. Keep looking for a mechanic.
Otherwise, plain-jane, non-locker, non-nodular 9" 28-spline center sections can be readily bought around here for a hundred bucks or so. I doubt the market is drastically different in Tennessee. Check the auto part swap meets or run a wanted ad on Craigslist. Or if you don't want to fool with any of that, you can get a direct bolt-in 3.00:1 9" center section from WCCC for under $200.00. You should be able to pay for that by selling off all the truck axle parts you've accumulated.