The only thing worth upgrading back there is the rear lower control arm for camber adjustment. And I wouldn't bother if the front is at stock or stock-ish camber (read <-2 degrees).
I'd say save some serious cash and buy used parts but it sounds like it's too late for that. People dump their OE stuff that still has new car smell on it for peanuts around here.
http://www.ft86club.com/forums/showthread.php?t=107788
http://www.ft86club.com/forums/showthread.php?t=104599
http://www.ft86club.com/forums/showthread.php?t=103889
I've seen OE toe links and LCA's and other bits and bobs as well, just nothing recent.