I also use Feline Pine in the litter boxes. You may be able to find cheaper wood pellets to use as well. I get usually a 10lb bag of Feline Pine at a time and it lasts me a long time. You don't need to use a ton of the pellets in litter boxes. They expand as they get wet so a little bit can go a long way. I've tried a lot of different litters and this is the one that I've found to be the best so far, for inside the boxes at least.
For outside my litter boxes...well my bunnies have their own room lol. Their flooring consists of everything from fleece blankets to low pile rugs to Sisal rugs to linoleum to plastic mats. One of my bunnies won't walk on the linoleum though, it's too slippery for him.
If your bunnies chew regular rugs could you try low pile or Sisal rugs? Sisal rugs are made out of natural plant fibers so if your bunny chews them a bit it's not the end of the world. Or low pile rugs, I think often sold as indoor/outdoor rugs. The fibers in the rugs are really short so it's harder for bunnies to get their mouths around pieces of rug.
I use these in one part of my bunny room too...
They are really cushionie and I'd guess good for the bunnies feet. My bunnies like to run around on and sleep on them. But you'd have to watch to make sure they don't chew them (mine don't, luckily, I provide them with lots of better stuff to chew on).
If you're just looking for something for the flooring inside a cage I'd recommend using fleece blankets. They are comfortable for the bunnies, and pretty absorbent if they do have accidents on them. Bunny poos you can just shake off the fleece and you can throw them in the washer to clean them or hand wash them too. Fleece isn't a stringy fabric like some others so there's no loose threads to get nails caught on or anything like that. You can usually get it cheap as well, try looking at a craft or fabric store in the sale or clearance section.
Wow I didn't mean to write that much, lol sorry about that.