In general when looking for the cheapest flight to Cusco, try to book your flight during the month of March for the best deal.
In general, most flyers find the cheapest time to book a flight to Cusco is about 58 days prior.
In general, booking your departure to Cusco for a Monday represents the best deal on airfare. Try to avoid a Thursday departure to stay away from the highest prices.
On average you can find the best deals on plane tickets to Cusco when looking for flights with morning departure times.