Once you are talking about a system that can support scale, the fact is, jumping up to the next size doesn't cost anything in the grand scheme of things.
If you are taking about a steam driven still house, what's the all-in price difference between a 125g setup and a 250g setup? Nothing. What's the difference between a 250g setup and a 500g setup? Nothing. What's the price difference between 125g and 500g? Minimal.
What's the cost of upgrading? 2x, more even when you consider the downtime. God forbid you size a boiler and cooling for a 125g setup, you've got to basically tear