When I first started quilting, I bought fat quarters and half-yard cuts of fabric I liked, even if I didn't know what I would do with it. Then when projects started coming to mind, I switched to yardage for setting squares and triangles, borders and backs. Now I just buy what I need to fill in when I absolutely, positively can't find what I need in my stash.
As for the price, cotton is a commodity and last time I checked, our federal government pays hefty subsidies to U.S. cotton farmers, which distorts the true market price as well as supply. Wish they'd get out of our business!