I currently have 4 Lionheads and 2 litterboxes. Rabbit droppings are very high in nitrogen so I have a bin outside that I dump the litterbox "contents" into-and voila! In the spring, I have wonderful fertilizer for my gardens. Of course, I only use wood pellets, hay (which I pick out before dumping) or rabbit pellets for litter. I line the boxes with newspaper (which is thrown out before dumping, also).
The hay is the cheapest filler (but a little messy inside and doesn't absorb smell)
The rabbit pellets are the cheapest
The wood pellets absorb smell the best