Get your carpenter m8 to build one, it'll be cheaper!
That way you can also spec up how you wanna be sitting (you may want some tilt), the width, etc.
You could visit a scrap yard, and grab yourself the car seat of a Rover 2800 (old model car!) or such like. These have some wicked springs on the bottom and are really comfy (a friend has one as his easy chair !
). You could then attach something from the base that come up between your legs as a steering column and you could have a kind of table to place the steering kit on. Now that sounds like a cheap, comfy and very bizzare thing to do!