I stumbled on a Harbor Freight when I was up in Albuquerque, next door to a LQS I had been in. They didn't have the blade packs, but I did get a carpet cutter with 3 blades - all for $3.99. I threw the cutter away after taking out the blade. I figured that $1.33 per blade was a bargin compared to $7.49 at Hobby Lobby. Probably should have bought all the cutters while there!!!! I'll get to go back in February and May, so maybe it will be me who buys out the blades! :)
I have not noticed any difference in the blades.