Are you crafty at all? There's a very easy way to make them if you can find the fabric you want. fabric + stick on velcro (or sew if you want to get fancy) and some scissors. All you need.

Childrens Place has capes and masks for $8 - guessing that's too much though.

Not $2 but not bad:

http://www.orientaltrading.com/superhero-cape-and-mask-set-a2-14_1185-12-1.fltr?Ntt=capes

Etsy?

Is this for a party?

I made capes as a party favor a few years ago......

Take 1 small cheap bath towel. Sew a big button on 1 corner. Sew elastic loop on opposing corner. Decorate as required.

If you do not want to do a button - purchase velcro.

Ebay

I did a web search..couldn't find any online retailers. Maybe call/try Dollar Tree?

I heard Target carried them for $2 or something cheap like that (nothing fancy, plain silk cape), but I've called every single one and none seem to have any. I need to get about 15. Any suggestions would be greatly appreciated!