Here's some answers that we came across with regard to your question.
The estimated cost of sending humans to the red planet is roughly 500 billion U.S. dollars, though the actual costs are likely to be more [1]
The U.S. National Research Council's 2014 report gives a rough estimate of how much it would cost to get astronauts to Mars. The effort is the equivalent of "perhaps 75-150 'flagship class' robotic exploration spacecraft (assuming an average cost of $1 to $2 billion each)," [2]
Anfimov suggested that the entire project would cost $20 billion and added that Russia would contribute 30 per cent of these funds.[3]
References
- Taylor, Fredric (2010). The Scientific Exploration of Mars. Cambridge: Cambridge University Press. p. 306. ISBN 9780521829564.
- Mike Wall, Space.com (June 4, 2015) : A Manned Mission to Mars: How NASA Could Do It - How much would it cost?
- Will Knight, newscientist.com (8 July 2002) : Russia proposes manned Mars mission by 2015
