Just looked at GameStop's values on iPad 3 trade in: 
16GB Wifi- $317.75 credit , $254 cash
32GB Wifi- $380.25 credit, $304 cash
64GB wifi - $442.75 credit, $354 cash
16GB at&t- $380.25 credit, $304 cash
32GB at&t- $505.25 credit, $404 cash
64GB at&t - $624 credit, $499 cash




http://www.gamestop.com/recommerce/web/ChooseDevice.aspx?manufacturer=Apple&family=iPad
16GB Wifi- $317.75 credit , $254 cash
32GB Wifi- $380.25 credit, $304 cash
64GB wifi - $442.75 credit, $354 cash
16GB at&t- $380.25 credit, $304 cash
32GB at&t- $505.25 credit, $404 cash
64GB at&t - $624 credit, $499 cash
http://www.gamestop.com/recommerce/web/ChooseDevice.aspx?manufacturer=Apple&family=iPad