It really depends on where you live, who you're going with and where you go shopping. If you are going with your friends $70 sounds about right. But if you're going with a boyfriend/girlfriend the...
NYC is a very expensive city. You should bring at least 700$ for a 3 day stay at econo lodge in the heart of times square for 1 person. For personal spending like souvenirs, 300$ is very good.
At least $50, no more than $100. You want the girl to enjoy themselves, but you don't want to flaunt your money, otherwise, you will look big-headed, egotistical, and arrogant.
The amount can vary...