May I ask what reasoning/evidence lead you to that conclusion? I'm sort of viewing it as a trolley problem: I can either kill my immortal self, or I can terminate 28 other lives that much sooner than they would have.
(I'm also realizing my conclusion is probably "I don't do THAT much charitable to begin with, so let's just go ahead and sign up, and we can re-route the insurance payoff if we suddenly become more philanthropic in the future")
Look at it in terms of years gained instead of lives lost.
Saving 28 lives gives them each 50 years at best until they die, assuming none of them gain immortality. That's 1400 man-years gained. Granting immortality to one person is infinity years (in theory); if you live longer than 1400 years then you've done the morally right thing by betting on yourself.
Additionally, money spent on cryonics isn't thrown into a hole. A significant portion is spent on making cryonics more effective and cheaper for others to buy. Rich Americans have to buy it while it's expensive as much as possible, so that those 28 unfortunates can ever have a chance at immortality.
From Mike Darwn's Chronopause, an essay titled "Would You Like Another Plate of This?", discussing people's attitudes to life:
Conclusion, graphs, and references in article. As usual, I recommend reading Chronopause.com as Darwin has many good articles; to quickly link a few: