As an international seller I hear your pain. Items over 100g are extremely expensive to ship via conventional post services.
I do a few things to keep the cost down to
maintain my competitiveness: For my small purses I try my best to control my weight to make postage of $5 possible. (normal registered air mail) Occasionally I went over because of the packaging but I shell out those extra.
For my larger bags I am sure to lose money on shipping even when I put $10 as the cost, but I make that up by pricing slightly higher, and I encourage people to combine ship orders when they buy more.
When you are shipping more than 200g, courier services like DHL becomes more affordable if you can find the right connections to get the corporate rate.