It's not going to be exclusively available for ultra billionaires, if it is possible at all. There are lots of things that would be powerful advantages if only a tiny elite had access to them: vaccines, antibiotics, anti-retroviral drugs, digital computers... but if a thing is demonstrated possible at all, others will figure out how to do it again. And if the first inventors refuse to sell or share the technology it will just be spread by the second or third group to figure out the trick.
Consider the cost of polio vaccine versus the cost of keeping a polio victim undead for a year in an iron lung. It's ineffective medical treatment that really costs. Even if you don't care about human life, even if money is your only preoccupation, we need life extension technology to stop the cost of end-of-life care from bankrupting modern society.