Go to the internet and search for padded mailers (or padded mailing envelopes). It will bring up several sites. Here's a few that I found.

PLUS, check out the ebay auctions for padded mailers. I think you can beat these prices (and some offered free shipping).

Esther

http://www.papermart.com/Product%20Pages/Product.aspx?GroupID=4459&SubGroupID=4460&ParentGroupID=19011#4460
7 cents / 250 per case

http://www.packagingsupplies.com/padded-shipping-envelopes.html
about 10 cents / 500 per case

http://www.uline.com/Grp_31/Padded-Mailers?Pricode=WD873&utm_source=Bing&utm_medium=cpc&utm_term=padded%2Benvelopes&utm_campaign=Envelopes%2B%2F%20Mailers
about 14 cents /250 per case

http://www.nextag.com/padded-envelope/compare-html
about 11 cents / 250 per case

http://www.papermart.com/Product%20Pages/Product.aspx?GroupID=4459&SubGroupID=4460&ParentGroupID=19011#4460
7 cents / 250 per case