The estimated price tag for a good shot at implementing SENS and demonstrating robust reversal of aging in mice is $1B: $10M/year for ten years in each of seven research programs, plus some padding.
I'm not a billionaire (yet), but that's why 100% of my charitable donations go to the SENS foundation. Every marginal dollar has a much higher expected utility there than anywhere else that I've found.
Industrial Progress is a very important and practical cause, and this group has a very effective leader who is actually having some effect at persuading people (particularly people in industry) and providing them with better ideas. And it's cheap. SENS needs a billion. A few hundred thousand would be huge here.
I second this recommendation, CIP has been doing an amazing job at showing how and why industrial progress is amazingly beneficial to human prosperity, while dispelling the common critiques the "green" movement uses to dispel this idea.
Both SENS and CIP are hugely important ventures that people should look into in my book.
You can do a lot more awesome engineering and science and exploration if you don't die after ~80 years.