FYI, if you use stamps.com, you can print first class postage at home. They even have a free trial period, I believe. For Priority and above, you can use USPS.com.
The days of cheap ($4) international shipping are gone. When the USPS raised their international rates, the base price for the smallest first class "package" rate (1 or 2 oz) went up to $6.16. From sending many international packages through the post office here, they won't let you send a bubble mailer as an envelope or letter. You also want your bubble mailer to be large enough to attach the small customs form (about the size of a 8.5x11 sheet folded in half, or 8.5x5.5).
The price of international shipping for flat rate Priority mail boxes is about $25 for a small box, $60 for a medium box, and $80 for a large box. From the US to Canada, it is slightly cheaper, with the small box at $20, medium box at $40, and large box at $60.