I've found great deals on Ebay. Usually they have been on damaged packages of name brand blades. They are not always available, though.
I tried the carpet blades at Harbor Freight. It was a waste of money, but maybe I just got a bad batch.
Premier blades from Amazon were recommended, but I found them to be less than great. So far, all but one has started out with a "nick". I'm not sure that is the correct description. What I mean is that it skips right out of the package> I find that particularly irritating, as I don't realize that the fabric is not cut completely, move my ruler and then find out it's not cut. Then you have to go back and try to get your ruler back in the same place and it never works. I will not buy them again.
bkay