@KoiwiGal - It's usually not so bad on big tours, because if you really don't have much money you can just give whatever you can afford. The smaller, more intimate tours I wouldn't want to go on without a good-sized tip handy.
I actually didn't end up spending all that much when I was in New York City. I stayed in a hostel, which was more expensive than most of the other hostels I've stayed in, but still cheap enough, and offered free breakfasts and other perks. I mostly ate street food, which isn't too expensive and should be a part of a NYC experience anyway. And I networked a little bit among other backpackers, so I ended up doing lots of free activities, including the Shakespeare in the Park show that was on at the time.
New York can be expensive if you want to see all the famous New York City attractions, but there are plenty of things to do that don't cost anything.