I've seen many people do it and I currently keep 2 females in a 18X18X24 Exo-Terra. So far they have been doing well. I'd highly recommend keeping an extra setup, such as a simple tub enclosure in case of a fight. It does and will happen at the most inconvenient time. If you can be prepared for it your animals will benefit from it greatly. The biggest things to keep in mind are to provide a feeding station for each female as well as numerous hides so they can get away when they need "their time."

I paid $100 for my enclosure with a light, add another $50 for three females and it sounds like a good deal as long as you like their traits.