Having the option to purchase a kidney, privately would not only increase the donors, there would be less recipients on the waiting list to receive a kidney as they become available from a death. Also, many would benefit greatly from selling a kidney. Definitely worth consideration. However, paying for placement on the waiting list as it is, should not be an option.
For those opting to buy a kidney should not be included on the waiting list at all, instead participating in a living donor program designed to match needs and then submit the offer to the donors agency/broker/lawyer or whatever. This would benefit many