The cheapest litters are usually woodstove pellets and pelleted horse bedding- these can be made of hardwood or softwood (such as pine).  Because of the manufacturing process that the pellets go thru the heating that is involved in making them eliminates the harmful phenols that can bother bunnies.  So these are cheap litters that in my opinion work great.  I have used woodstove pellets since I got my bunny a year ago- the pellets are a bit thicker and heavier than Yesterdays News or Feline Pine- but have great odor control and the slight size increase of the pellets is not an issue for my bunnies at all.  I think I pay about $4 for a $40 bag.

Woodstove pellets can be found at home improvement stores such as Home Depot, Menards and at the stores that sell the stoves usually too (specialty stores) and horse bedding can be found at farm supply stores and other types of feed stores that carry other horse supplies.

I use Feline Pine, it’s way cheaper than YN. I keep looking for WSP, but can’t find any anywhere… grrrr…..