How much fabric you looking to buy? For small projects I look for interesting skirts and dresses at thirft stores and re-use the fabric. I can find interesting embroidery and otherwise pricey textiles at a fraction of the cost otherwise. I often find saris too which provide about 6m of fabric.

check with relatives..... They were the ones who invented the phrase, "She who dies with the most fabric wins" I collected some fantastic bolts from my aunts. Also my granmother gave me baskets full of yarn and threads.

I have also found that you can get extremely good fabric in the form of sheets.... go to kmart or some such store and get a 100% cotton sheet for 4 bucks. you can then dye it any color you wish or just leave it white etc. but you get fabric that is wider than what you can get in a fabric store and you get more of it for less money.

garbtheworld.com is a website run by stay-at-home moms, they sew costumes and clothing and they make some really cool cloaks and robes! nice fabrics, heavy cotton and fleece and stuff.... they give away big boxes of their scraps for FREE, all you have to do is pay for it to get to where you are. they even will cater to specific requests if they can. worth a look! :)

You're in Los Angeles? Check out FIDM's "Scholarship Store"- they have a lot of neat clothes to destroy (usually for very cheap) and their entire back room is filled with fabrics, also for very cheap.

I sometimes find those really big curtains at goodwill in really cool fabrics for only a couple bucks.