Depends.
I mean, Shade is a bounty hunter who has a shady connection to a major pirate organisation through Amara Faell. Maybe the Black Void grabbed a shipment once, or maybe Amara used the group's wealth to pay for a treatment for Shade as a gift. Or maybe Shade just saved for a while for a treatment.
And then you have the owner of the robot bartender on New Texas, who presumably is making a fortune. New Texas is a "tourist" planet, in the sense that the main area you visit is a touristy area. New Texas is also a planet that appeals to a certain type of visitor - one who quite wealthy. Its noted at one stage that Steele got the invite to visit New Texas quite earlier than a lot of others. Makes sense, New Texas would be the kind of world that would want new inhabitants to be quite wealthy. If I remember correctly, Big T says as much. So the guy who owns the bar on New Texas is either a successful business own or a tourist who has invested after coming to the planet. Probably both.
If the general population could afford this treatment, you're making something that
isn't in short supply,
isn't difficult to make and
is easy to distribute. Which makes no sense. It makes far more sense for the anti-aging treatment to be a regular dosage than to be a one off. Its a luxury in a dystopic, hedonistic setting. And that's something that you can make a lot of money off of.
If its in short supply, you're making demand for it. If you're making a demand for it, you're calling the price.
If its difficult to make, it takes time and resources to produce, leading back to it being in short supply and again, allowing you call any price you want.
If its difficult to distribute, well, to use a real world example, there's a reason why botox should only be handled by a professional.
Any one of those allows for a ridiculous price jack. And it allows for it to be something only affordable to the rich (or super rich depending on how much of a dick you are).
Why make one treatment when you can make it last a lifetime.