Two decent drivers in the two main cars for every event, then whoever can afford the third seat on a per-round basis. If no one pays, no third car.

Still not a fully-fledged manufacturer team and the car won the drivers and teams titles in 2017, so M-Sport has the right to charge top dollar for anyone who wants a seat. That's how you get some return on investment, especially when M-Sport has only managed to (so far) sell one of the current-spec cars, vs. many of the pre-2017 Fiestas.