You probably should post your brand of cutter to make sure that it takes other blades. A few brands do not.
Instead of the Harbor Freight blades, I look for good blade buys on eBay. This way I get name-brand blades (and quality) but at a much more affordable price than say at JoAnn's (even with a coupon).
Blade sizes are specific to the cutter. I only buy 45mm blades for a 45mm cutter, for example.
You might want to advertise on your local Freecycle group for fabric and batting donations. Ours allows one ad per week. I personally don't think it is worth keeping track of fabric costs unless you are making tons of quilts; it's really a tiny tax break. If you can build up a stash of donated fabric, that would be much more worthwhile in terms of saving money.