Sure, you can preserve someone for that amount, but revival, once it exists, would probably cost the equivalent of millions of dollars, and who would pay for that?

It's trite but it's true that you usually 'get what you pay for'. So that if cryonics really only cost $300 a year, I wouldn't go anywhere near it. But then I know that it is hugely subsidized by people who obviously have a genuine interest in it working, so this is inconclusive.