Well, people in the old portal version on mobile got up to like, 70 or something. I'm pretty sure PoC even in our version is technically infinite.

Unless you want an extra handful of blueprints THAT badly, the only reason you'd ever need to spend 7000 on it to get to stage 50 and beyond would be in order to beat the rank of that other whacko who spent 7000 oil on it to get to 50 and beyond. At that point anyone crazy enough to go that far probably deserves the ranking rewards to go with it anyways.