> starts charging monopoly prices, and buys any new competitors for 100x earnings so that it can retain a monopoly, including paying commpetitors not to enter the field at all.

This kind of mustache-twirling evil plan is insanely expensive. As in insta-bankruptcy expensive. Plus you'd have all kind of things backfiring, like business moving away because their rent, or their employees' rent are too expensive.

> Now, let's say I want to run a monopoly like that.

By all means, go ahead, I'll buy your properties at the foreclosure auctions.

The only way you'd be able to make your evil plan work would be with the support of a government. (With someone else paying the tab.)