Cyclonechuah: There are generally 2-3 countries in the world that will have extremely reduced prices for original games for localization reasons. One of them is Thailand (Which can get you games for as low as RM 30).

As JuzJoe, these games are usually region locked (Meaning you can't play outside of the country they were meant for) and considering MW2 is a Steam game (Meaning you need to be online to authenticate it), its probably region locked.