My guess would be that, overall, the VW has had the most money put into it. However the majority of that would have been from VW motorsport themselves prior to pulling out of the WRC. Hyundai must be fairly close behind too, that car was developed for a few years as WRC car.

In terms of being made specifically for WRX then GCK must be the biggest single outlay, most of the other cars have started from a base from someone else but the Megane is built from the ground up.