average cost to rebuild rear differential.

Well fellas I dumped some maintence moola $$$ into my recently purchased 2006 doublcab six speed 4x4 trd, Im just trying to run a tight ship here you know what im saayyyinnn. Most of the organs I picked up on the black market craigslist, I got practicaly new headers and y-pipe, and a 2 piece drive shaft for 500$$$ The exhaust stuff took care of my engine codes I was throwin, but the noise I have been hearing while driving has not went away. When i went to throw the new shaft up I realized it was about 3/4 inch shorter then mine so I salvaged the carrier bearing and threw it on mine which my old was wore out, and got all new greasable u-joints and slapped it back up there. Next I took all of your guys advice and spent about 200+$$ on redline mt-90 and 75-90 hoping and praying it would work, and it did with shifting but the sound remained. It will whine on deceleration and dissapear when i press the clutch and coast. I pretty sure the noise is not the tranny but in the differential, like a pinion bearing or something. so my question is what should i expect to pay for a rebuild with possible gears and have them change my wheel bearings while there in pullin stuff. I do not have the LSD and no locker. any help on my situation would be Great. and PS if anybody needs a drive shaft I will sell it 250 and u pay shipping.