There is a very nice little custom step mill going for a song on eBay. It's a 6"x6"x2.5" unit completely assembled and tested, it just needs a spindle, motors, controllers, and software and the bidding is currently at $200!
I know this guy and he knows his stuff: The machine is sweet! He started the auction at $1 and is selling this unit to guage interest. He has made quite a few of them on his larger, homebuilt, machine and wants to get into the business of makeing them for sale.
Check it out, if I had the space, I'd buy it for that price!