Genuine PS2 games and consoles, together with MP3 players tend to be a lot more expensive in Turkey than in the UK (we're taking 2 PS2's with us to Turkey as presents as they are half the price here!!).
Be careful if you are tempted to buy new cinema release DVD's as the quality is sometimes very poor and you will only find out once you are back in the UK. Also, last year a lot of the shops selling fake DVD's were raided by the police and their stock was taken - not sure what they would do if you were caught at the airport with these.
Anyway, that's the word of caution out of the way. Expect to pay about £3.00-5.00 for a DVD (latest cinema releases) and about the same for PS2 games. Avoid the market sellers and ask to see a demonstration (if possible) before parting with your money.