[blah_why_not]

bucket + [your choice of: sawdust, leaves, dirt, sand, etc.] --> bury it every few days, or chuck it in a dumpster

[zdragnar]

Animal bedding (pine shavings, essentially) works wonders, and is very inexpensive.

[Scoundreller]

wood pellets, but buy them from the hardware store for a fraction of the price of what the pet store sells them for. Dunno about the horse store.