You can see Broadway and Off-Broadway shows for free by working as a volunteer theater usher.
Except For The Non-Profit Theaters, Broadway Is For The Professionals
Most Broadway theater ushers are part of a union, meaning that those theaters can't accept volunteer Broadway ushers. The exception is with the non-profit theaters, notably the Roundabout Theatre Company. Roundabout has two theaters on Broadway, Studio 54 and the American Airlines Theatre. If you are interested in volunteering as a Broadway usher for a show that's playing at either of those theaters, the thing to do is to go up to the box office during normal hours and inquire at the window. In most cases, they will have a sign up sheet where you can pick an open date and put your name down for the performance that you would like to usher at. These slots can fill up fast, especially for popular Broadway shows, so best to sign up to usher as early as possible.
Off-Broadway and Off-Off Broadway Theaters Need UshersAlthough Broadway doesn't offer much choice for would-be volunteer ushers, the rest of the New York City theater scene is a hotbed of opportunity. Many Off-Broadway and Off-Off Broadway theaters are happy to have volunteer ushers work their shows and then see the performance for free. There are too many theaters to name that accept volunteers, so your best bet is to drop by or call the box office of the theater where you would like to usher and ask what their policy is. A quick web search will usually help you, since many of the Off- and Off-Off Broadway theaters post ushering information right on their websites.
The Job (and Reward) of a Volunteer Theater UsherVolunteer ushers are generally asked to arrive at the theater 60-90 minutes prior to the performance, at which point they will be given instructions by a member of the theater's regular staff. Sometimes the volunteer ushers will help "stuff" programs (i.e. add inserts) and do some light work to help prepare for "opening the house" (i.e. getting the theater ready for the audience). Once any necessary prep work is done, volunteer ushers are generally assigned some post. This may involve showing theater patrons to their seats or checking tickets, but more often than not, volunteer ushers will be given a simpler task, such as greeting audience members as they enter the theater or pointing them to the restrooms.
Once the audience has been seated, volunteer ushers will be permitted to find an empty seat and enjoy the performance. They may also be asked to stay after the show to help clean up discarded programs and trash from the theater floor, but all in all it's a pretty easy gig with a big payoff - great New York theater for no cost whatsoever. It does appear though that no programs exist to bring back previous volunteer ushers, so you have to reapply every time you want to do it - but it's a great way to avoid paying for high-priced Broadway tickets.