I just use the post office's click and ship program on the USPS website. Since I have an account with the post office to obtain my priority mail shipping boxes, I can just log in to that account. First class package international is available using that service. You pay with a credit card, but otherwise it's a lot like PayPal shipping - but with more options.

You have to manually update the shipping/tracking info over to PayPal, though.

https://reg.usps.com/entreg/LoginAction_input?app=GSS&appURL=https://cns.usps.com/labelInformation.shtml