To people that want to save money with fabrics, I'd like to remind that even linen and curtains indeed are fabric, and those can be extremely cheap in second-hand-stores while still being very good quality!
And of course, people tend to throw away sheets/clothes/etc if they get damaged in some way, but a good little craftbabbu can always cut away the remaining good parts and use them for small projects, completely for free.
Actually, from personal experience, linen and other bed-sheets from second-hand-stores tend to be a lot softer and more comfortable against skin that new-new fabrics, as they have been washed and used possibly quite a lot, thus leading to the fabric becoming soft and lovely (and you won't feel so bad if you make mistakes with that fabric, since it wasn't as expensive!)
Also zippers and buttons can be a pain in the ass to buy, and you can never be too sure if there comes a sudden project and you can't just go to the store in the middle of it. I usually cut off the zippers and buttons (and button-hole rows too) from old clothing that would otherwise be thrown away (mainly because I don't like the fabric enough to take the whole deal). It's good to take all of them and just store them in a bag or so, so you'll always have a bag full of zippers and buttons to choose from! Especially for hidden/invisible zippers, the color doesn't even have to match too precisely, since it'll be hidden anyway.
Same goes for all kinds of decorations on things, like embroideries on pillowcases etc.
For a fine example of how you can use things in imaginative ways;
I got a small-ish tablecloth (the waxy kind) from my Granny since she didn't need it anymore. It ended up becoming a raincoat for my little sister, since she really liked the pattern. Sewing waxcloth is easy and it's just as waterproof as the actual raincoat-matrials, just a bit more stiff! Another fine use for it could have been making it into an umbrella, but I didn't have a base for that, shame.