There are options from other cities as well if you head to Google Flights instead of ITA's search. For various dates in March, Volaris has $200 roundtrip tickets from New York City or Los Angeles to Mexico City. Volaris also has roundtrip tickets from Chicago for just $222. Interjet has a few select dates from Las Vegas to Mexico City for as little as $192.
From Boston, you can make the trip for $233 with American and from Washington D.C. tickets are $260. Meanwhile, Delta will take you from Nashville for as little as $272.
That price on quality airlines is good excuse to get out of town and see a beautiful city with a lot going on. As always, those prices could be gone quickly, so ping a friend and do something spontaneous.