Fabric can be really expensive, I have put together a few ideas of how you can find fabric for very little money.
Duvet Covers - If your find a duvet cover that you like it can be easily cut up and used for your project. I recently reupholstered a chair using a duvet cover.
Off Cuts - most fabric stores have a section or a bin where you can buy remnants of fabric, you can get lucky sometimes and find a relatively big piece.
Old Clothes - Old clothes are great for projects, if you have an old pair of jeans you can cut them up and you have some denim which you can use in a project.
Table Cloths - Look around in £1 shops for cotton table clothes I found some in Poundland for 50p each. They are great for small projects.
Charity Shops - Charity shops are great if your looking for more expensive fabrics ie. Leather you can find old coats which you can cut up and use.
Hope This Helps!