Where do you find vintage fabrics—aren't they really expensive?
Yes, often they are. And, if you look in the usual places, you'll often find that vintage fabrics just aren't in your budget. Or you paid so much that you can't bring yourself to cut into it and actually use it to make something. I have a few like that :)
So, what can you do? Definitely keep an eye out on Ebay because you can still find bargains. But expect competition and don't fall in love and get into a bidding war. Serious collectors, especially of feedsacks, will pay lots of money for what they're after! But the cool thing about fabric is that tastes are very subjective—everyone likes different things. I found these two fabrics recently—one a more traditional floral with roses and the other a mod stylized floral. No one bid against me. And both are 2 yard lengths so lots to work with. I'm experimenting with simple bags and have a need for larger quantities these days.
But the best advice I have is to expand your definition of fabric. Look for tablecloths and napkins, curtains, old quilts and coverlets, pillowcases and sheets—there's a lot of fabric in sheets!
I was shopping at an antique mall a few weekends ago and found a bin of half-price linens. Mostly junk except for a 1960s orange and pink striped pillowcase with a pink edge. 50 cents! When I got it home I soaked it in Oxyclean for a bit, washed and dried it, then cut it up. I got almost a yard of fabric from the case and another nice piece from the edge. Sweet!
I always find tablecloths at flea markets and especially like the printed heavy cotton ones from the 50s and 60s. Even if there are stains, you'll still have tons of fabric to work with. At least enough for a pillow or apron or bag. Well-made curtains often have deep headers and hems. Once you let them out you can easily get another 1/4 to 1/2 yard of fabric.
And, if you're into quiltmaking or use patchwork in your designs you have even more options. Look for smaller fabric items like dinner napkins, cotton clothing, and tea towels. I got this funny fabric with houseflies from a little girls dress at a flea market in Connecticut. It had a tear anyway so couldn't be resold as a dress, but I got a nice sized piece—enough to make a tissue cozy with a few scraps left over for patchwork.
You can certainly spend a lot of money if you want to (and that goes for most things) but there's always a less expensive solution if you keep an open mind!