In your example the treatment simply becomes too expensive with a slim chance of success. The relevant situation is one where a treatment is readily available

In your example the treatment simply becomes too expensive with a slim chance of success. The relevant situation is one where a treatment is readily available (no assumptions about cost are being made) but covered by a patent, thus keeping the doc from using it because someone legally (= on paper) keeps the doc from using the treatment method. And yes, patents are about money and property rights and richness. Not about treatment cost.