71 GSS seems to be thinking straight. Build the chassis/cage to go 250. Then it is not an additional cost to work up from say 150 with more power. Engines, well they are almost like brake pads and rotors, expendable items.
The first steps are working with tech to build the appropriate chassis/cage. Then build an engine to work on licensing. Once you get licensed for 130 the rest is just steps on the path, expensive steps mind you.