Urk! You're not kidding about their stuff being ruinously expensive. If anyone decides to make their own and is looking for natural fabrics and even ready made layers (particularly dyables), Dharma Trading Company is fabulous. If you want to splurge and go for silk, Thai Silks has reasonable prices and a great selection. If you want to try your hand at designing your own fabrics, an inexpensive way to start is to get a basic set of Derwent's Inktense pencils and/or blocks (available for a helluva lot less at Dick Blick and Amazon). These are best used with fabric medium and set with a hot iron to ensure the colors don't fade quite so badly and there are tons of Youtube videos on using these. I'm going to pick some up one of these days...

Sorry about the edit to fix the coding. :-}