Let someone pay 20,000x the price of a good or service if they want to. This is a good thing, not a bad thing. This drives early returns on investment, leading to cheaper and widely distributed drugs in the future.
Say you got a million (or 10 million) people to pay extra (it'd be lot of people at that point); the manufacturing demand wouldn't go up any, and they would probably just delay delivery of some other doses for a week (or a month).
1) The money would go to the manufacturer.
2) The supply limiting factor can be addressed in a reasonable timeline
3) The demand will exist at the time when supply is increased.
4) The price is a limiting factor.
As far as I know, lead times for this drug manufacturing equipment is usually >1 yr and the demand will not be there when it arrives. All of the vaccines currently cost $2-20.
The other option is paying with tax-money...
btw, another view: why fix it to 20,000x? why not auction?