Some ideas for the category engine...
Maybe Supercars could dust-off the 5.0 Repco-Brabham engine (I never knew there was such a thing!):
Or something from a manufacturer that stills exists, the 4.0 Judd DB (an 8-cylinder derivative of the Judd V10):
670bhp @ 10,000rpm, worth it for the sound alone:
https://www.youtube.com/watch?v=j1DQ9f_VEAg 
I'm not sure that going to a gear-driven quad cam racing engine would cut costs, but you never know!