Or you can attach a $350 E300 Razor scooter to your chair. Significantly cheaper, and involves little work to modify.

http://m.youtube.com/watch?v=r56tYri_1Hc
http://m.youtube.com/watch?feature=plpp&v=SB_Zl5LUuEo

I can confirm that the hinge idea works with a Tilite footplate and a Razor scooter...my son was very happy when I came up with that idea!

And for longer range, you can always add another couple of batteries.