At 500hp, you can do an RB cheap, and a LA motor
maybe a bit more!! You increase the power levels,
you increase the build costs.
At these increased hp levels, you'll have to spend more, regardless of block sizes. Oiling systems,
must be upgraded due to the increase in engine rpms. Better heads to support that level of horsepower and stronger bottom end pieces, especially the RB. The bottom line is that both the small and big blocks will cost some coin to build at 550-600 hp. If the ECONO route is chosen, then big blocks would have a "slim" margin in price difference to their advantage, power wise, situation may be reversed with the small block outpowering the big block. Strokers are a completely different story, though this thread compares stock stroke motors.