"The rich got rich. The poor got even-- poorer"
-Catch 22's "Permanent Revolution"
That quote is modified off of some other quote which I feel like a bad scholar for not remembering who said that initially, but anyway, that really doesn't matter that much.
Anyway, there are a bunch of theories on this. Yes, probably only poor communities, and the stray hippy, would probably actually donate organs under these conditions, but this could not necessarily be viewed as so much of a necessity of the poor, but rather the deus ex machina for the poor.
Organs, on the black market, go for exorbitant amounts of money. This is given based off of the various risks that one goes through to procure such an organ. Even given that legal stresses were eased and legal selling of organs was allowed, the price for saving a life would be quite high.
The rich and the opulent are often very concerned with the ability to use their wealth, and thus the truly wealthy would not be opposed to dropping TONS of money into prolonging their life of relative obscurity. On the other hand, this gives a poor inner city family an opportunity to start over and move up in the world and completely change their life stories.
Besides, you only need one kidney to survive, so they would still be able to live a perfectly normal life, granted maybe with a bit more of a consideration on personal health.
The big theory now is that supposedly pigs have surprisingly similar organs to humans, so many believe that raising genetically altered pigs to harvest for organs may be the most "ethical" option as to getting plentiful, cheap, third party organs. We'll see how that works out. I mean, we all know that Mad Catz products are crappy. What happens when we start buying the Mad Catz equivalent of kidneys?