The next best price is $333 on American, so this is over $100 savings.
Flights departing Chicago on Mondays-Thursdays
Flights departing Washington, DC on Wednesdays and Thursdays.
Check date availability on Google Flights and use those dates to book on Priceline , free cancellations within 24 hours of booking)
Using Priceline, my sample travel dates: May 3-10, 2017 (IAD-PTY-IAD) and April 3-10, 2017 (ORD-PTY-ORD)
Please note that while this fare is valid at time of posting, fares can fluctuate in a matter of minutes/hours/days.