What, one of these scorpion type vehicles or a kit car?
Pricing depends on alot of factors including the kit your purchase, drivetrain used, complexity of the kit(partial turn key, full assembly, etc). Also if the kit is based on a donor car how much is required from that particular car, and of course what car it actually is.
I’ve assembled numerous kits for people from RCR, Ultima, F5. They can start as low as ~10K for a resonable kit and you’ could have $30K into it before it’s all said and done. Some kits come with gelcoat GRP bodies which do not require paint, others need that legwork. The F5 GTM uses C5 donor parts(suspension, steering, brakes, etc) so part availability isn’t that bad. Gearboxes are often the single most expensive piece of the car, ranging ~4K for a refurbished audi or porsche box upwards of $30K for a medeola, quaife, or hewland sequential.
Assembly time in a serious kit car can run upwards of 200 labor hours in something like an Ultima or RCR Gt40. Other kits can be shipped in and rolling out within a week or two.
The bike powered kits such as depicted in this thread, are substantially cheaper to build due to the drivetrain used. Most of them come as partial turn key, requiring only minor suspension assembly, drivetrain install, and wiring. Working non stop, you could have one up and running in mere days and for minimal cost with a proper donor bike.
My own small kit car will be slated around $15K in GRP/kevlar(20K in carbon kevlar), partial turnkey +2K, and includes quaife gearbox. Will just need choice of wheels and donor bike to run 