here are some base value prices...
viva pinata -$3
wet - $7 (or was it 9)... i think that it was 7... pretty sure 7
fifa world cup 2006 - $1
dark sector - 1.50
lego indiana jones - less than $1
also, i visited two gamestops, and they wouldn't let me trade in games that are sealed in front of them... they said to open it [while not in the store] and come back tomorrow... it's their policy... and these two gamestops were extremely far apart, one in brooklyn and the other in queens new york... what's up with that???