The Freecycle Network (TM) is composed of over 5000 groups and almost 9 million members around the world. It's a nonprofit, grassroots organization that gives away things for free. If you need a prom dress, first join the Nassau or Suffolk chapters for free, and then write a post, explaining what you're looking for.
Also, if you have a gown or dress or anything else to donate, you can post that on the chapters' sites for free as well.
Head over to the site and type in "Nassau" or "Suffolk" into the search box and you'll be brought to the appropriate website.
Becca's Closet has chapters throughout the U.S., and there are multiple locations in Brooklyn.
Throughout Nassau and Suffolk counties, you can find lovely prom dresses at bargain prices. You might have to look around to find your size, but once you've tried on that fancy dress of your dreams, it'll all be worth it. These thrift shops are also great for finding accessories to go with your beautiful dress.
This famous auction site carries all kinds of items and if you type in "prom dresses," you'll find both new and gently used formal gowns or cocktail dresses at prices that are a fraction of the cost at many bricks-and-mortar stores.
From H&M to Target and more, you'll be able to find deals and steals at some of Long Island's department stores. And don't forget to check out places like the Tanger Outlet Centers, where name brands are sold for much less than in regular stores.
Rent a Prom Dress for Less
Why buy a prom dress if you're only going to wear it once? There are sites like Rent the Runway where you can rent designer dresses at much cheaper prices than outright purchasing one.
Prom Girl lets you know where you can purchase prom dresses at a discount online.