Except once you price out buying a track lock, gears, and install you are paying close to the price of an 8.8. My friend andrew blew out his 7.5-twice- with a auto 3.8 with basic bolt ons.
OP- if you can find a solid, complete rear for 300 or less, its a good deal. try to find one with 3.27's, your stock gear. then you can simply swap in if you dont plan on changing the gears immediately with no ill effects. but be careful- some 99's came with 2.73 gears.