(Note: Introducing designer Alec Holland who is jumping into the online fray and contributing some good dirt on the Left Coast.)
There are some great places to find high-end fabric at low-end cost, you just need to tough it up, and venture into the black hole that is: Downtown LA's fabric district.***
The seemingly billions of fabric stores can be daunting, so skip right to HOME FABRICS (910 S. Wall street between 9th and Olympic. 213.689.9600) which has the best selection of silks, brocades, and cotton velvet I've seen. In the back of the store you can find unbelievable mohair for 35 bucks a yard...try finding that anywhere else! They also have a great selection of inexpensive cording and trim.
The other go-to store is one block over. MICHAEL LEVINE (919 S. Maple Avenue between 9th and Olympic. 213.689.1363). There are two MICHAEL LEVINE stores across the street from each other so don't be confused.
One is upholstery and the other is fabric and notions, but check it out as well, because they have some great heavy cottons and suiting wools. The upholstery store walls are lined with beautiful fabrics at good prices but it's the center isles that are filled with bolts of great fabric for as low as $6.00 A yard. You'll have to dig a little, but it's always worth it. AH
*** The way to make this a successful trip is to know about the SECRET $3.00 PARKING. When on Wall street, between 9th and Olympic, go down the ally towards Maple Avenue to find the lot. You wont find cheaper, it's directly between HOME and MICHAEL LEVINE, and you don't have to worry about searching for those hard to find meters that need quarters every ten minutes. It makes the trip downtown a snap. Good luck!