I use wood pellets for a wood stove. It's all natural, no accelerant it's cheap I pay $4 for a 50 pound bag. stuff is called pennywise wood stove burning pellets
I also use the breeders choice cat litter, that is recycled newspaper pellets. As everyone has mentioned, they absorb urine & odour really well. I get mine from Animal Tuckerbox or Petbarn. You get a big 30 litre bag for $18 to $20.
I wasn't very happy with breeder's choice for Bandit, too smelly. I switched to Oz-Pet cat Litter which is a compressed wood pellet. Costs the same amount, but I get more use out of a bag I reckon and there's less smell compared to before
Wood stove pellets, $4/40lb. Cheap and plentyfull. I used to use the newspaper pellet cat litter but found it too pricey and my rabbits didnt notice a difference.