I think you may be able to get $35, probably more. Once you trade in 3 PS2/GCN/XBX games, you get an extra 30% added onto the trade in value. This is running at Gamestop.
My estimates:
Rayman 3 - $6-7
Jak II - $12-14
NFL Street - $11-12
ZoE - $6-7
Def Jam Vendetta - $5-6
That's without the 30% added on.