Tickets aren't really difficult for any sporting event in NYC or around (Giants, Jets and RedBulls all play in New Jersey which is a short train ride from the City to the stadium), it's just a matter of what you are willing to spend.
Giants and Jets (NFL) will definitely be the most expensive but you will be able to find them on secondary market websites (Stubhub, Gametime app, Seat Geek etc)
During November the MLS playoffs will be going on. NYCFC and the RedBulls will most likely be in it. NYCFC plays in Yankee Stadium and the RedBulls play in a soccer specific stadium in NJ which is a short train ride (the path train) from the City. Red Bull arena really is a fantastic venue, it's just in the middle of no where, not much to do around the stadium, I guess that's where NYFC beats them as the stretch of bars outside Yankee Stadium is pretty fun. Those tickets shouldn't be that bad, even if the playoffs probably between $40-50 a piece, maybe cheaper for NYC because they have more seats.
The Knicks (NBA) and Rangers (NHL) are always on the more expensive end as they both play in Madison Square Garden. Especially if a good team is in town. I've seen Cavs-Knicks tickets in the nose bleed section for over $100 before.
Then the 2 cheapest options would probably be the Nets (NBA) who play in Brooklyn, The Islanders (NHL) who also play in the Brooklyn, the same venue that the Nets play in (Barclays center) and the Devils (NHL) who play in New Jersey (Newark). The Devils have a really nice arena but it's in Newark, not too sure you wanna be there late at night, and not like you will be going out around the stadium either. Where the Nets and Islanders play in Brooklyn is a really fun area with tons of bars and restaurants around it and for some pretty crappy games (Like Nets vs Hornets) I've seen tickets in single digits (between $8-$9)
All of these on secondary markets like Stubhub, SeatGeek, Gametime. All phone apps which will give you the ticket right there and get you in. You could probably go through the teams for these as well but the more expensive ones will most likely be that expensive because the team has sold out of tickets. For the cheaper tickets (Nets, Islanders, Devils) you'll probably be paying more than what's on the secondary market.
If you have any more questions don't hesitate to ask.