Well it depends why it costs a few million per person. If the production of the vaccine takes thousands of tons of coal and hundreds of pounds of bark of a slow-growing tree then yes, we don't have that per person. But if the current million dollar price is to enrich some pharma investors then there's nothing to say that society needs to find $100 trillion to enrich someone.

Not everyone has cancer. And the price is sort of likely to come down if there is a technique that reliably treats cancer.

You can't just multiply the cost for 1 person by the number of people in the population. If it's mass produced it will be a lot cheaper.

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.