Robin Hanson quotes research which finds that blood donors aren't really put off by the prospect of being paid for their donation, they just don't want cash. Vouchers would work just fine, though.

Commenter Michael Keennan then comes up with this ingenious idea: instead of refusing to compensate organ donors at all due to ethical concerns, why not pay them back in kind? How about, for example, giving kidney donors free health insurance for the remainder of their lives? That would surely cause more people to consider donating their kidneys, which may save plenty lives; and I don't see how it raises any ethical dilemmas. Doesn't it seem fair and just for people who have donated an organ to receive free health care in return? Doesn't it seem more unjust if they do not?