I once tried generic blades from an Amazon re-seller & they were junk. Good for cutting paper-backed fusible web & that's about it (same as my used Olfa blades). I sometimes will buy blades from JAF (on sale + additional 10% off with VIP card since I belong to AQS), but usually I find better deals from Amazon merchants. I just make sure they are Olfa blades in the original package. I buy 5 at a time & that lasts me for one quilt, or sometimes I'll buy 10 if it's a better deal (more than that is too expensive for me).
I only splurge on 4 things: fabric, thread, hand applique needles & rotary blades. Everything else I buy as cheap as I can find it or make my own. There just isn't anything like the feel of a brand new rotary blade slicing through freshly pressed fabric.