Mame, you can buy this Tracfone for $10
You can buy a 30 minute airtime card for $10, or a 60 minute airtime card for $20. Look at the pay-as-you-go airtime cards on this page.
That particular phone gives you double minutes--so, if you buy the 30 minute card, that will give you 60 minutes of talktime on the phone, and, if you buy the 60 minute card, that will give you 120 minutes of talktime.
You can order the phone from Tracfone's Web site and then buy the airtime card on their Web site after
you get the phone. On their site they tell you how to activate the phone and add airtime.
Immediately after you buy the airtime card online, you just follow some simple instructions and the airtime you just purchased is automatically added to your phone.
When they ask where the phone will be used, give them area code 212 that's Manhattan. The area code doesn't really matter--you can make nationwide and international calls on these phones. Tracfone has very good service.
And, should you need to add more talktime to the phone, while you are in NYC, you can easily do that.
I hope you have a great time in the Big Apple.