(Okay, we'll try to stop saying Benjamin.) For the results, Kayak looked at both domestic and international round-trip flights in economy class; evaluating search dates between July 1, 2016 and June 30, 2017 for travel dates in that same period. Of course, What are the cheapest days to fly? is a complicated question.
A Russian Soyuz capsule usually takes at least two days to rendezvous with the ISS, because of the carefully timed dance of manoeuvres that must take place for a spaceship to safely meet the orbiting laboratory. Using a new launch process, three astronauts have now made the trip in just under 6 hours.
The average distance to Mars is about three times the minimum and would take three times as long. Getting there is only part of the problem, braking and landing will also take a long time! The last NASA flight took 7 months for the trip and 6 months to get into orbit. Read some Edgar Rice Burroughs.