> Where is the limit to how much money is expended on one person?

It depends on what would be an effective and indicated treatment.

> What if they have a 99% likelihood of death, are unlimited funds expended in this case?

Then treatment would neither be effective nor indicated. But if it was your parent, your child, your granny, wouldn't you rather they at least try?

> What if there's a shortage on drugs - who should get the limited supply available?

The people for whom treatment is most likely to be effective

> Which country with public health options pays for biologic medications or similar patient-tailored solutions?

The UK, for a start.