Sadly from the manufacturing process description alone, we are going to be decades away from when it's actually ...not a few million dollars per individual to treat.
Maybe another way to ask is: On the scale from 400k of white-shoe lawyer-hours, to 400k of custom 7nm silicon-etching, where should I mentally place this? The former isn't going to budge, the latter will cost pennies in a generation's time.
[1] https://www.genewiz.com/Public/Services/Gene-Synthesis/Turbo...
a) do a biopsy of the tumor and some healthy tissue, which is fairly cheap,
b) do genetic analysis of those samples to find the differences. This used to be prohibitively expensive, but now is fairly cheap too, the price went down six (!) orders of magnitude since 2000,
c) ask specialized software to find the optimal protein set to express. This software can be used for all the patients around, so cost of development will be split among them,
d) synthetize the correct messenger RNA and embed it in lipid nanoparticles. Not cheap, but not prohibitively expensive either, this is basically a biological equivalent of a printing job,
e) check the resulting drug and send it to the clinic where the patient is treated.
This all together is a much more straightforward and automatized process than extracting tumor-invading lymphocytes from a patient and babying them in vitro with a lot of attention from human scientists and use of fairly expensive reagents. The price tag for this process per se should be at least two orders of magnitude lower.
Then you must add the original development and testing costs, amortized equipment cost and profit. This is where the total price tag may balloon.
It would have interesting implications if in the future a family could invest in a bank of mrna molecules for their future generations. A new form of wealth.
If it's $40,000 yeah -- still that's on par with the cost of an ER visit for a traumatic injury and a couple of days as an in-patient, exactly the sort of thing you have insurance for.
A treatment that costs a few million dollars now will cost a few thousand dollars in a decade or two, assuming all costs scale according to the Carlson curve. In practice, this is probably a bad assumption, if nothing else because a hospital bed alone costs a thousand dollars a night or more, but it does seem likely that mRNA-based treatments will become much cheaper to develop over time to the point where they will be cheap enough to be viable by the time they would actually finish passing through the regulatory hurdles.
Edit: I have no clue why people would rather something not exist than for something to exist but for it to be too expensive.
e.g. if you want to pay a chemist to synthesise Aspirin in a lab for you it will be very expensive. But it costs pennies in the store.
I don't exactly know the breakdown, but it must skew towards the old & sick -- like cancer patients. It's not inconceivable that million-dollar cancer treatments could become widespread.