You could use polar fleece as an outer, but it's not as waterproof as pul. Otherwise you would just buy two covers and make loads of nappies and inserts.

I've made some using bamboo batting (used for quilting) and cut up old towels and tshirt lying around. You will need Velcro and some elastic too. The fold over elastic is my favourite but again not at all spotlight stores. You can do a seam though and thread normal elastic though.

It's really easy to make nappies, but they aren't as good as some if the store bought ones with the fancy fabrics, but you just have to change bub more often. You will save loads of money though!