In order for humans to get to Mars, a spacecraft of great engineering would need to be built, one that would certainly be the most expensive vehicle ever made by man. In the movie, the Martian, a spacecraft called the Hermes is used to get between Earth and Mars. The thought of travelling to Mars has been questioned for decades, with Walter Hohmann proposing an elliptical orbit between the two planets. The movie shows the Purnell manoeuvre which shows a slingshot effect to get to Mars in a short time (it travels at 12,000mph) , the large spacecraft is not powered by chemicals, since they produce a large thrust in a short period of time, and an ion drive would need to be used. This will give gradual thrust over time and will last longer periods, currently these drives are not powerful enough to power a spacecraft like the Hermes, but it has been used successfully in the Dawn Spacecraft.
The stated downside of such an ion dive, which accelerates at 2 millimetres per second, is that the trajectory would need to be measured through a computer system, as any uncertainty could cause a major accident. In the movie it would take 124 days to get from Earth to Mars, through the ion drives, but NASA estimates a vessel would take 6 months to get to Mars. Whilst this technology is in its early stages, there is a lot of promise in how this could be vital for travel in space technology in the future. At the moment they have an efficiency of 60-85% and it is 10-12 times (according to NASA) more efficient than a chemical thruster that has been used in older spacecrafts.
The cost is the greatest factor of a spacecraft capable to travel to Mars. The price would be estimated at above $100 billion, and with a maximum of $500 billion. These figures are extremely excessive with relativity to NASA’s current funding, it equates to around 30 years of government funding to even begin a small scale production of the Hermes’s technology. The material that the Hermes would be built of, would need to shield it's passengers from radiation and the sun, a lack of this could have harmful effects on a human. If we look at the ISS, it cost $150 billion at the time, and it was incredibly advanced, but the Hermes would topple the ISS in terms of magnitude and technology. At the moment SpaceX is the closest we have to the Hermes, and Elon Musk is striding towards making Mars colonization a reality and he is taking the initiative towards that.