1. We can't tell you how much airfare will be without knowing where you are coming from. Airfare varies considerably based on departure and destination airports, and dates of travel. Use a travel search engine such as Kayak to look that up.
2. Airbnb is illegal in NYC. Cheap hotels right in Manhattan will be $150 and up a night, more on the weekends. Most hotels will be $200 and up. However, many NYC hotels will require you to be 21 to check in, so you'll be limited to the ones that will allow an 18+ check-in.
3. Food is generally more expensive in NYC than in other places, even fast food. That said, you can eat pretty cheaply if you stick to food trucks, fast food, and pizza. But the nicer restaurants and the touristy spots will cost you more. We can't estimate your food costs without knowing where you plan to eat.
4. We can't estimate your shopping money because we don't know what you are going to buy. You can get cheap touristy souvenirs in Times Square for relatively cheap. But NYC has some of the best high-end shopping in the country, so you could easily spend $500 on a shirt if you wanted.
5. What you spend on tourist places will depend on what you do. It costs $30+ to visit the observation decks. You can visit the Statue of Liberty and Ellis Island cheaply ($18.50 per person, to visit both islands) if you just want to tour the islands and not go up in the Statue or take any behind-the-scenes tours. The 9/11 Memorial is free to visit, but there is a charge for the musuem. There are admissions fees for most of the museum in NYC, although some of them allow you to choose what you pay (they don't advertise this though). There are hop-on/hop-off bus tours that are a good way to just see things, and they start around $45-50 per person for a one-day ticket. If you want to see a Broadway show, you can expect to pay quite a bit for that, depending on your show; there is a TKTS booth in Times Square that sells discounted tickets for same-day shows, but you are limited to what shows they have available. You can window shop for free, wander Central Park for free, visit Times Sqaure for free...but most attractions will cost you, and they aren't cheap.
In short, we really can't esimate a cost for you because we don't know what you're going to be doing. And that will determine how much it's going to cost.