Precisely! Same thing as currently with access to vaccination and vitamin D.
How much has the cost of a heart transplant gone down since its invention in 1967?
Realistically though, we have a pretty good idea of what we're looking for. We don't know the exact combination of chemicals that cures aging, but we know it's going to be a combination of chemicals, and we know we can mass produce those.
I get a med that's $18k every three months, for a mililiter of fluid. I wouldn't have a hope of paying for that without health insurance, and I'd expect health insurers to be resistant to covering mega-expensive life extension therapies.
Generally, the more common diseases are cheaper to treat, because the burden of development, IP etc. gets spread across more people.
Medications for ubiquitous stuff such as high blood pressure tend to be comparably cheap, unless they are a fresh novelty. And aging is even more widespread than HBP.
Estimated at 2-3% of the world population, so 100M+ people.
I am sorry to be prying such information out of you, but things with such a cost label tend to be very high-tech (e.g. tumor-invading lymphocytes etc. that need to be cultivated for each patient separately, which cannot possibly be cheap).
I suspect it'll look cheap in comparison to life extension treatments.