I'll do this by tiers based on your own store's prices with whatever I find on the website:
Games to buy for $10 or under:
Condemned: Criminal Origins-$9.99
Marvel Ultimate Alliance-$9.99
Just Cause-$9.99
Project Gotham Racing 3-$7.99
Games to buy between $11-$20
Gears of War-$17.99
Ninja Gaiden II-$17.99
Prince of Persia-$18.99
Forza Motorsport 2-$12.99
Project Gotham Racing 4-$14.99
Guitar Hero III-$14.99
Tomb Raider Legend-$14.99
Earth Defense Force 2017-$17.99
Fatal Inertia-$12.99