elliptical hybrid bicycle?
 

elliptiGO elliptical glide bike - outdoor elliptical trainer overview
Maybe combine that with a HSD-based hybrid system?

TWO GRAND!!! :eek:

Healthy profit margin there!

Haha that is a healthy profit margin. Not too shabby for a bicycle

You might be surprised at how easy it is to spend money making something light enough for human power, and getting it to market.
The odds of selling many bicycles without seats are not very good, either, IMHO. I'd electrify a velomobile, or at least a recumbent, if I wanted a better bike to start from.