I don’t care about any particular artist enough to require a huge amount so you’d mostly be paying me for the inconvenience of remembering to follow through for 50 or so years.
We’re looking at something like one annual salary because anything less won’t make enough of a difference to bother with the effort for half a century.
I think it’s fine to pay some for it.
I don’t know how your healthcare system is structured. But let’s assume there is a profit motive in getting you to donate blood. Let’s also assume profit is a problem. So we want to reduce profits.
If you get €25 per donation that is €25 less profit for them per donation.
The demand for blood is going to stay the same. No one will decline a live saving surgery because it’s a bit expensive and will pay anything to get it. Increasing supply will decrease profit margins.