What a bargain! I found these flights on Kayak and they can be booked on Webjet.com. Only $360.11 USD (roundtrip, including all taxes and fees) from Miami to Cuzco, Peru. The flights I found were departing November 22nd and returning November 30th. It would make for a quick trip, but certainly enough time to head to Machu Picchu from Cuzco. There would even be time to hike the Inca Trail. I found several flight options available both with long and short layovers.
Trusted Travel Girl Bonus Tip: The flight shown above has a 7 hour layover in Lima, Peru. This should allow ample time for you to venture into Lima for a late night dinner or a brief trip to Plaza de Armas before taking off for Cuzco. Additionally, there is a hotel in the airport if catching a few hours of sleep sounds more appealing.