Using off-the-shelf components and a little electronic know-how, you can build your own self-balancing scooter for a fraction of the cost of a real Segway unit. It makes me wonder, really, if there's not a market for a gizmo like the Segway with a more reasonable price tag.
The only thing the prototype is missing is blue LEDs and maybe some spikes. Oh, and some barbed wire--it needs barbed wire. A Mad max version of a Segway just sounds like a lot of fun.
(Thanks to enoelie for the link...)