I always ask that and never get an answer. It's the age old dilemma. I want 1,000 horsepower, with power everything and AC, but it needs to idle at 500 RPM like my Kia while getting 40 MPG.
It just doesn't happen that way. Unrealistic expectations have ruined many a build.
IMO if you can't afford the fuel it takes to horsepower than hit the links. It doesn't matter how you do it because it takes roughly .45 pounds of fuel per horsepower per hour.
That means 1,000 HP takes 450 pounds of fuel per hour or 500 HP needs 225 pounds of fuel per hour. It is what it is.
Most fuel waste on these engines is from NOT running a vacuum advance and not cleaning up the cruise carb tune.