Might still be reasonably priced if/when it's available in countries other than the US?

Specifically, countries that don't have a broken extremely-overinflated-pricing model for health care.

CAR-T (programmed t-cells for blood cancer) are around $400-500k not including the cost of harvesting and implanting them back into the patient.

Yeah $20,000 seems very cheap for such a treatment.

Also there are biohackers who synthesize their own insulin and even COVID-19 vaccines and test it on themselves. Their work may cause them more harm than good, but it's their bodies and they're free to experiment on it however they choose. When somebody has a terminal illness and is facing imminent death the risk calculus is very different where even taking the bargain basement biohacker version of a medication may make sense. (Though obviously this particular treatment is a bit different because it uses a modified HIV virus)