On Amazon you could buy the same games for similar prices but CeX happens to have lower if you can visit one of their stores, which honestly is better than ordering online (unless it's the only method to obtain that one item).

There are loads and loads of very reasonable priced games (albeit they might be missing the manual or the cover might not be in the best condition which is why it's better to check in store). I've recently got into buying PS2 games because they're so cheap and worth it.

The games:
Gran Turismo 3 - £0.50 - https://uk.webuy.com/product.php?sku=711719276227
Gran Turismo 4 Prologue - £0.25 - https://uk.webuy.com/product.php?sku=SPS2GRAE002
Gran Turismo 4 - £2.00 - https://uk.webuy.com/product.php?sku=711719617358
Gran Turismo Concept - £0.50 - https://uk.webuy.com/product.php?sku=SPS2GRAE002
Grand Theft Auto 3 - £1.50 - https://uk.webuy.com/product.php?sku=5026555300490
Lego Star Wars - £2.50 - https://uk.webuy.com/product.php?sku=5026555300490
The Getaway - £0.75 - https://uk.webuy.com/product.php?sku=711719432524
Spider-Man 2 - £2.00 - https://uk.webuy.com/product.php?sku=5030917023002
Splinter Cell - £0.25 - https://uk.webuy.com/product.php?sku=3307210126306
Freedom Fighters - £1.00 - https://uk.webuy.com/product.php?sku=5030930031343 (the Xbox version is 80p though)
True Crime: Streets of LA - £1.00 - https://uk.webuy.com/product.php?sku=5030917022128
Pro Evolution Soccer 4 - £0.05 - https://uk.webuy.com/product.php?sku=4012927025420
Max Payne - £0.50 - https://uk.webuy.com/product.php?sku=5026555300629
Hitman 2 - £0.75 - https://uk.webuy.com/product.php?sku=5032921017374
Final Fantasy X2 - £2.50 - https://uk.webuy.com/product.php?sku=5030930037017
Killzone - £1.50 - https://uk.webuy.com/product.php?sku=711719691945
Prince of Persia: Warrior Within - £0.75 - https://uk.webuy.com/product.php?sku=3307210181497
Manhunt - £3.00 - https://uk.webuy.com/product.php?sku=5026555301534
Soul Calibur 2 - £1.00 - https://uk.webuy.com/product.php?sku=5030930034900
Mercenaries - £0.75 - https://uk.webuy.com/product.php?sku=023272663254
Killer 7 - £3.50 - https://uk.webuy.com/product.php?sku=5055060923016
King Kong - £0.50 - https://uk.webuy.com/product.php?sku=3307210196811
Oni - £0.75 - https://uk.webuy.com/product.php?sku=5026555300209
Teenage Mutant Ninja Turtles - £4.00 - https://uk.webuy.com/product.php?sku=4012927023938
Teenage Mutant Ninja Turtles 2 - £5.00 - https://uk.webuy.com/product.php?sku=4012927025833
Teenage Mutant Ninja Turtles 3 - £12.00 - https://uk.webuy.com/product.php?sku=4012927028193 (currently out of stock)
Spy Hunter - £0.10 - https://uk.webuy.com/product.php?sku=5037930070136
Soul Reaver 2 - £1.50 - https://uk.webuy.com/product.php?sku=5032921013635
Star Wars: Racer Revenge - £2.50 - https://uk.webuy.com/product.php?sku=023272998660
Genji: Dawn of the Samurai - £1.00 - https://uk.webuy.com/product.php?sku=711719164210
Mark of Kri - £0.75 - https://uk.webuy.com/product.php?sku=711719435426
Primal - £0.75 - https://uk.webuy.com/product.php?sku=711719413929
Giants Citizen Kabuto - £0.75 - https://uk.webuy.com/product.php?sku=5026102005830