Megazorb is almost the same, just smaller pieces,and is alot cheaper If you can get hold of that you'd get alot more for your money. I used Carefresh for my hamsters but it was way too much so I changed to Megazorb
Is your bun indoor or outdoor? I use Carefresh but I only use it in the litter trays along with straw and newspaper as mine are indoors. It's great stuff but would be expensive to line a whole cage with. I saw a sample of Megazorb last weekend, it's the same as Carefresh but much smaller pieces and it's cheaper. You can get in online at The Hay Experts, they have lots of other wonderful stuff for buns there as well. Someone else might be able to tell you if there is anywhere else to get it from.
I used to have vetbed to line my cage and sometimes I would put a layer of newspaper over that, the great thing about vetbed is that you can just stick it in the wash time and time again. You can get oval shaped vetbed from the hay experts but if you search online you should find somewhere that sells it in all sorts of sizes and loads of different colours. I bought double the amount I needed and cut it into two pieces so that when one was in the wash I had another to hand. I've made a large NIC cage now which is lined with carpet tiles and has a separate liter tray but I still keep the vetbed as it's good for poorly buns or if they've had an operation or just a nice fluffy comfy thing to rest on.
Sorry me again, just realised that megazorb is primarily used for horses so if there is an equestrian centre or supplier near you then you might be able to get it cheaper from there.
There's an equestrian centre near chessington, near the hook road arena but not sure if it's any nearer you? The pet suppliers you mentioned could possibly sell it so worth a try if it's easy enough to get to.