Ah yes, the constant struggle to enable an even more literal exploitation of the poor by the rich.
You can't get out of acute money problems with a tax break. Arguably still more appealing to the lower middle class than the upper class, but it seems literally impossible to reward people for the sacrifice involved in an organ donation without the marginal utility problem arising.
Still, I think it eliminates all the truly unpalatable failure modes, like impulsively donating a kidney to pay off a gambling debt. If some people choose to make an organ donation so they'll have more of their income over a five year period to invest into their children's college fund, that isn't such a bad thing.
The law, in its majestic equality, allows rich and poor alike to sell their internal organs to try to make their power bill payment next month.
That's without explicit coercion (sure, I'll do X for you, so long as you sell your kidney).
We all buy things daily from entities with much more power than ourselves, for example.
Hypothetically, if someone wants to sell a kidney to pay the bills, and they are of sound mind, the government shouldn't stop them.
That is rhetorical, it is highly unethical. And similarly, desperate people will sell organs under financial pressure and limited or no regulation on the sales tactics or accurate disclosure.
A more effective plan would be to offer $100-$1000 cash payment at time of registration when getting a license to be an organ donor. It is hard to find matches. Better and more economically efficient to have a broader pool of potential donors, for all parties. And since the donors are already brain dead, no ethical dilemma.