A new startup company called Moonfish finds cheap deals on flights leaving out of Philadelphia International Airport, writes David Murrell for phillymag.com.

George Zeng, a Wharton MBA grad and former engineer at Facebook, started Moonfish when he noticed major fluctuations in flight prices. He designed a search engine that finds the best deals by tracking prices on every flight departing from the airport over the next year.

The catch?  You have to fly out of Philadelphia and you need to be flexible with your preferred travel dates and destinations—the website spits those out for you to find the lowest fare.

But once you’re good to go, you can find great deals—like flying from Philly to Barcelona for as little as $200 round trip, or 80 percent off the regular fare.

You can sign up at Moonfish for free, or pay for one of two premium subscriptions — at $1.99 and $19.99 a month — which give you access to the most-discounted flights.

“The way I think about how to get cheaper fares is basically to build in flexibility to your travel,” Zeng said—the dates you travel, where you’re leaving from and where you’re going.

Read more about Moonfish here.

[uam_ad id=”62465″]