I would recommend against using a fulfillment service - they cost money and just aren't necessary for a lot of smaller projects. Comics have such small margins that it doesn't make sense to cut into your own bottom line.

Buy padded envelopes in bulk ( Uline or Amazon are fine, but there's probably a local supplier who's cheaper ), and a label printer. The Brother label printers come with a program called P-touch, which allows you to import data sets from Kickstarter into customizable templates.

We're based in Canada, so we used ChitChatsExpress, a US broker to do international shipping. In Canada, Packages below 500g and a within certain sizes can be mailed as a letter instead of a parcel, which is vastly cheaper. If you're states-side, there's probably a broker or service that will help reduce the cost of international shipping.