I may be entirely wrong here...

But there used to be 'international postage coupons' that could be purchased. If you're in the US, you should be able to either go to the local PO or call and they can give you an idea of prices to different countries (if in fact they are different).

Personally? I'd figure out how much profit you're looking to make off of each CD sale (sorry, not on MP3 so I don't know what the margins are), and figure how much you can afford to discount off of the median postal cost and make that a standard charge for "out of country" customers.

Remember also that if you ship them yourself, proper CD mailers cost a little bit, and you'll probably need some form of packing material as well (I used to use very stiff cardboard inserts - mainly to attempt to keep the shipping envelope from folding and damaging the case.)

M