Hi Anthony, Sigma is the best place I know to buy inexpensive proteins.

Thanks!

At this time we are buying from Sigma. I would like to see if there is a source that is less expensive (focourse for the same purity).

You could try Worthington. They mostly sell enzymes, but they have good purity and are not expensive.

http://www.worthington-biochem.com/index/catalog.html

What do you require the proteins for? If it's just for SDS-PAGE, order plasmids from Addgene (about $10 each) and make your own :)

Alternately, Bio-rad, Sigma, GE, Life Tech etc sell gel filtration standards - these tend to be packs that include 4-8 purified proteins and cost about $300 - $500

I hope that helps!