I dont think there is a way to make F3A more affordable, the entry classes sure are as cheap as you like, (nobody needs a full 2 meter ship to start in pattern)

so I think YS developes engines for F3A and that means state of the art and only the best possible.

I beleive there is no reason for a cost efective YS 175 running on petrol, the same reason there is no need for a F1 car to be more economic to run