Where are you situated? That will help a bit.
Options in the states sometimes include CVS, Rite Aid and Walgreens, but not always.
You're limited to carbon steel, Stainless and PTFE coated stainless.
All the info and more, right here: http://badgerandblade.com/vb/showthread.php/292388-Single-edge-blade-guide
Personally I prefer PTFE coated, box from Ted Pella via a want-to-buy on the BST. Can't stand carbons. Others may differ
I love the Treet carbon steel blades. I find them sharper than the GEM PTFE. I picked up 120 for $14 on AMZN a couple of months ago. With Prime, free shipping.
I use both the stainless gems and the carbon treet blades in my streamlines and find the smoother shaves come from the stainless coated ones.
although i think the carbon treet blades are sharper, but they do not last as long and as ever ymmv.