As we were climbing the steps from the subway at Coumbus Circle, we were approached by several people. We had a bit more than an hour, but not quite 2 hours, so when the guy from Bike Rental Central Park @ 57th St. approached us saying that he would give us 2 hours for 1, we said OK. We then had to walk 3 or 4 blocks to his shop, which was packed and it looked as if it would be a long wait. After waiting a bit, the guy comes back to us and tells us that "his manager" won't allow him to give the discount that he offered us. Its all a scam to get you to walk the few blocks past other closer places and when you get there, there is no deal.
I didn't want to give this company any money, so we walked back to the park and found an independent guy with bikes right there. Paid our money and were off, in 3 minutes.
Riding around the park is great. Just be careful what company you use. I wouldn't rent anything again unless, I saw the bike in front of me and saw the line.