In this month's issue of Mollie Makes magazine they mention a website called Spoonflower which allows you to upload your own designs to print on fabric, wallpaper and wall decals. I haven't tried it yet, but I'm pretty excited about the option to sew something with fabric I designed. I'm particularly interested in making prints for fabric dolls, like this one, where you create a template directly in the print: http://www.spoonflower.com/fabric/1452867
Prices look fairly affordable, (although my general self-imposed limit when buying fabric is usually $10 or less a yard). They start at $15.75/yd and $5 for swatches, eco-friendly textile printing and a range of 10 fabrics. Their help section explains pattern repeats, color guides for beginner designers. You also have the option to sell your fabric through them once you've uploaded it.
Hopefully I'll be trying this sometime in the near future, but if anyone reading this has already used it and has any tips to offer, I'd love to hear them.