In order to run a taxi in New York, you need a medallion. Because the number of medallions is restricted by the government (artificially restricting the supply, and thus, competition), getting your hands on a medallion can be extremely expensive. As Bloomberg Business explains:

“To own a cab in New York, you need a medallion—a metal shield displayed on the vehicle’s hood—and there are a fixed number issued by the New York City Taxi & Limousine Commission (TLC). Until very recently, medallions were a good thing to have a lot of. In 1947, you could buy one for $2,500. In 2013, after a half-century of steady appreciation, including a near-exponential period in the 2000s, they were going for $1.32 million.””]
On a more positive note (for consumers, at least), the competition in the taxi industry since the rise of Uber, Lyft, and other ridesharing services has decreased taxi ridership and significantly lowered the value of the medallions.