The pharmaceutical company Vertex sells the drug for $300k. Because CF Foundation helped fund the development, they get royalties, just like universities sometimes do when they help develop a drug.
This is great for CF because it’s mostly the insurance companies (and therefore healthy people) who are bearing the costs of the treatment.
So the CF Foundation is “forcing donatations” from the healthy populace through increased insurance premiums to bankroll their continued investments in treatments and such.
I don’t know if that makes it any more or less ethical, but certainly if it were mostly individual CF patients on the hook for the $300k (in aggregate that is — I’m not saying that never happens) then it would make less sense for the CF Foundation as a strategy.