The problem is base plate availability for sporty cars that are 4-down capable. Most MH owners tend to go for SUV/Truck/Econo style cars, so the demand for sports car base plates is low.
If you aren't tied to a specific car, it's probably easiest to go with something that has mass-produced base plates from Blue-Ox, Roadmaster, etc. Generally speaking, this makes life easier since the engineering has been done for you, and the base plates are relatively cheap.
On the other hand, if you have a specific car you want to tow, but there are no mass-produced base plates, you can go the custom base plate route. This will probably run $1-2k from a fabrication shop unless you can get Blue-ox/Roadmaster to do development on your car for a new product line.