Vet bed is different to fleece, it is an option but as you say its expensive.
Any fleece thats 100% polyester is fine. You can get them online, but I usually find that when you include postage its cheaper to buy them somewhere like primark, wilkinsons, B&M bargains, tescos, asda, Pound stretcher Etc.
However they do need washing 3 times without soft rinse before they work. And when you wash them generally, no soft rinse as this seals the fleece and stops it wicking away.
Same with whatever you choose to put underneath. Argos do matress protectors, or tescos. And towels can be tesco value.

The best pads Ive found are Dry nights bed pads for kids that wet the bed. If you cut one in half and turn it so the padded middle is on either end where they tend to pee these will do a 2x4 C&C. Given that they are £3 for 7 thats very cheap and cuts down the smell

but you can basically use whatever absorbant layers you like!
My set up is the dry nights, with a matress protector cut to size on top, then fleece. This lasts me 5 days (with a poo sweep daily), but my cage is large for two piggies, a smaller cage would need cleaning more often.
Hope this helps... Any other questions just ask
