I know it's not cheap. That said, if someone is willing to spend gobs and gobs of money to send a middle-aged couple for a Mars fly-by this would surely be orders of magnitude cheaper and far more likely to generate far more revenue.
Which doesn't exclude you from making a back-of-an-envelope calculation of the cost and a little bit of research, such as figuring out how expensive is a falcon heavy launch, and so on.
True. I could. In this case, I don't think one needs to go that far.
I know, with near absolute certainty, that it would be far cheaper to land 1,000 little robots on the Moon than to send two people to do a Mars fly-by. There is no way a fully automatic (no humans, no life support) Moon mission could even approach the cost of a mission to Mars with everything you need to support life and bring them back to Earth.
Part of engineering is to develop a sense for these things. After a while you don't need to resort to constantly calculating things to have an idea of the relative degree of complexity or cost of a project. This, I think, is one of those cases.
I know it's not cheap. That said, if someone is willing to spend gobs and gobs of money to send a middle-aged couple for a Mars fly-by this would surely be orders of magnitude cheaper and far more likely to generate far more revenue.