The issue here isn't that PhotoBucket are charging to host images. It's the no-notice change and the size of the charge.

Effectively they've knocked people off Ebay telling them that they can keep their sales for a one-off payment of £300.

If they'd given them two weeks notice then people could have evaluated the cost and decided if £300/year was a reasonable amount to pay, or if they should migrate elsewhere.

Doing it like this basically forces some people to pay up instantly. That's not fair dealing, that's rather more mafia-like.