I live in Brooklyn. I managed to find a place that'll sell you a used cylinder (that's right, it's yours, not rented) and they will also refill your tank.
The place is called Awisco, and they're located in Maspeth Queens. Frank is the guy that I know in customer service. You can give him a call (718-786-7788) and find out how much everything will cost.
Tell him Maria sent you.
P.S. The tank I bought was used, but in excellent condition, and it works very well.