Places I find GOOD fabric, new and old, stashes and notions, and unfinished projects than can be cannibalized for material-----
Flea markets and yard sales
Rummage/Community sales: prices are very low, as a rule
Goodwill/Salvation Army/Hospice/Church Thrift Stores: let them know what you are looking for, some may also have clothing unsuited for sale but salvageable. I volunteered at a church thrift store and found they toss items of clothing and also bundle unsalable clothing for recycling by a local relief organization. Volunteers could also purchase items at 1/2 the already low price. Men's 100 % cotton dress shirts in larger sizes are a gold mine of material.
Thrift Store bag sales: they manage merchandise with off-season bargains; all you can stuff in a bag for one low price.
Shirt/Dress Factories: there are a few left. Cut-off stacks are great, sometimes they have yardage sales, too.
Use your LIBRARY for patterns and ideas. Skip the magazines; you can buy a lot for the price of a subscription or issue. Most are designed to whet your appetite for the latest and greatest fabric, pattern, gimmick. (They're great eye-candy, I admit!)
Generations of American Women have had to make-do with whatever they could and made fabulous quilts. SCRAP QUILTS RULE!