Admittedly I'm the gal who hasn't used her rotary cutter yet (long story involving nerve damage) but the idea of finding something for a better price attracted me, so good for you!
Then I got curious and did some googling and found a blog where the gal mentioned, maybe she's even on this board, heck, I'll just copy what she said (after she mentioned Harbor Freight)
"Another source, with bigger packages of blades, is South Star Supplies - they have a larger selection. Harbor Freigh only has the 45 mm ones. Depending on size - you get 10 blades to a pack for $17.95 from South Star. Again - that wonderful price."
This was the website included.
http://www.southstarsupply.com/catal...products_id=66
Her other source for blades was Harbor Freight. Women, let's invade this man's world too! (if that gal is on this board, maybe you'd like to vouch for these too?)
This is her blog:
http://piecefulquillting.blogspot.com/