Abe, I don't know who is the cheapest now but here are a few links to bubble mailer suppliers:
www.bubblefast.com
www.shippingsupply.com
www.uline.com
www.browncor.com
www.bargainsgalore.com/bubblemailers.html
http://esupplystore.com
http://www.papermart.com/mailers_welcome.html
You should be able to find different quantities and features, self sealers, maual, plastic,recycle paper, bubble, Padded, sizes etc.