Least Expensive Way to Buy Canvas

OK, I've taken a big, potentially fatal step. I'm quitting my job so I can have more freedom to paint. I fully expect to have to be very careful about money for the first time in years. I'm going to buy, up front, extra supplies, and although I don't want 'bad, cheap' supplies, I do want to be as economical as possible.

I will be practicing, a lot, but don't want to use materials that would rule out a quality product. What is the least expensive brand/method for canvases. Is it cheaper to stretch your own? Is there a brand of good quality, pre-stretched canvases that would suffice?

I usually paint on canvases 24 X 24 and larger. (Don't like small portraits). So far I have used Fredrix pre-stretched, pre-primed canvases. A store in town has a buy one, get a second one for a dollar sale twice a year. I bought about 10 large canvases for around $400. I tend to start about five portraits at a time , and take a while to finish, where if I am able to paint more, I will, obviously, produce more. i.e. I will use up canvases very fast.

Any info/advice is much appreciated.

DeVon