We have 2 guinea pigs and I had read online about using fleece for bedding. As a mom who has made and used cloth diapers, it's not all that different. I had left over fleece in a container - just waiting to be donated or used.
For the absorbant layer I used an old beach towel for my first one. It's heavy but works. For my second one, I went to The Salvation Army Thrift store and got a bunch of old matress pads for $2 each. These are much lighter in weight when washed.
I also made them two "cozies" (basically a bag they can climb/sleep in).