Keep searching the Seattle Craigslist, there's been all kinds of Troopers on there lately, including a real nice, clean straight V6 Troop that wouldn't start, for $400. A wrecking yard would probably charge you more than that for just a tranny.

http://seattle.craigslist.org/cgi-bin/search?

Also note recent discussions here regarding converting a 4-cyl 4WD tranny for V6 use; a bit more work but if you picked up one cheap.............

'90 Troop 3.4 LS
'89 Troop RS (Has Valve Issues, needs Counseling)
HI, I'm Ed and I'm a Trooper-holic!
Keep On Troopin'......