VMware charges your per physical Processor for their software. They do not charge you per core, so the ROI calculator will use the same price divided by fewer processor cores.
I’ve found it is hard to adjust the ROI calculators to fit your environment and your goals. The best thing to do is compare the price of purchasing one server virtualizing say 10 servers to the price of purchasing 10 separate servers. That way you can get a ROI that better fits your environment.