Dude, even I'm not sure if it is the right place to post it to be honest and I'm a mod
I know interest checks aren't allowed as part of the F/S rules but this is a price check and those are fine in HEXUS.Hardware so I'm going to go out on a limb and say this is fine here too
What I tend to do is go through eBay, the F/S section here and CEX/Gamestations site and see who's charging what for what then work out what seems fair to me, I can't say what'll seem fair to you but I've just done the same thing with the games on your list and these are the prices I came back with -
Fifa Street 3 - £5
Modern Warfare 2 - £8/10
Sonic The Hedgehog - £10
NFS ProStreet - £6
Motorstorm - £5
Virtua Fighter 5 - £5
Burnout Paradise - £8/10
Tekken 6 - £10
Resistance 2 - £5
Killzone 2 - £5
Assassins Creed £7
Uncharted - £10/12
Hope that helps