Here's a weird one for you! My friend Nancy told me about this. It seems that Harbor Freight Tools sells a product for cutting carpet that takes blades that fit 45 mm rotary cutters. The blades are 2 for $1.99 (at least that's the price today).
I have no idea if the price will change or if they will always be available-- and I'm not sure if they are equivalent to the blades we get from quilt supply businesses. But they sure do look like they will work! If anyone has used them, or purchased from Harbor Freight, let me know. If they cut carpet, you wouldn't think they'd have trouble with cotton fabric. :-)