It's not quite the whole story. Medallions used to be almost free, which is why the waitlist was 10 years. They started charging 250k, but you can give them back for 200k.

From the MTA site: By capping the sale price of medallions, the MTA insulates medallion holders from market fluctuations, either up or down. When drivers want to resell, the price is what they paid, minus a 5 percent transfer fee. The agency said it is unlikely to cut the price. For those cabbies who paid nearly nothing for their medallions, the new sales system is an even better deal; they receive $200,000 when they surrender it for resale."