Check craigslist.com for your area, our 4-sale section, Prate4x4 or Marlincrawler forums for sale sections. You can usually pick up decent transmissions for under $200. Also, you don't have to get a G series transmission, you can also go w/the W series as well.

More than tread lightly. Leave it like you were never there, nor anyone else.
'90 X-cab 4.88's 33 BFG AT's, rr ARB, Headers, Ignition upgrade, cold air induction.
'91 X-cab 5.29's 315's BFG MT's, rr ARB, custom bumper and flatbed