There's an easy way to sort out overseas shipping, give them the package size and tell them to go to a package shipping service like www.shipito.com or similar (that's the one I use). You only charge them shipping within the states, then it becomes their problem. Most of those services have multiple warehouses within the US so even the local shipping can be cheap. But at the same time its a win for the customer too, because the shipping rates from those warehouses to overseas are usually way lower than you or even a normal retailer can get because of the volume they do. They put a mark up on their rack rate, and the customer still comes out ahead by a huge margin.
Incidentally, there are similar services in Europe that do the same thing to the US or where-ever, can save a lot of money on shipping.

Trev