Here's a look at completed listings on eBay for 60mm rotary cutting blades sold in lots:
http://completed.shop.ebay.com/i.htm....c0.m270.l1313
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As you can see, the price per blade can vary from over $2 to under $1.50 (not including shipping, which usually works out to less than $.25 cents a blade if sent priority). It depends on the day and who else is bidding.