I'll make it easy for you (just press, "sort by price ascending"):
10's:
http://www.partsexpress.com/webpage.cfm?&DID=7&WebPage_ID=3&ObjectGroup_ID=483&sm=1&so=2
12's:
http://www.partsexpress.com/webpage.cfm?&DID=7&WebPage_ID=3&ObjectGroup_ID=484&sm=1&so=2
15's:
http://www.partsexpress.com/webpage.cfm?&DID=7&WebPage_ID=3&ObjectGroup_ID=485&sm=1&so=2
I'd try out a Dayton Classic if you're really looking for something that cheap.