Lots. I bought a full sized bale of hay from a farm on Aug 30. It was finished last night, Then again, I have two dwarf rabbits and two young giants, and two guinea pigs.
For litter I put a thick layer of newspaper on the bottom and then a layer of wood stove pellets, enough to line the box, then hay. I usually use two 50 lb bags of pellets per year but I expect I'll need three this year.
If you live somewhere that gets cold enough to use wood or pellet stoves, the stove pellets cost $5 per bag in Canada, probably less in the US. I have to buy them all at once for the year because in my area they only sell them in fall and winter months.