How much longer do you think this planet will be able to support the exponential growth of the human population?
If present population trends continue, including both the first and second derivatives, the population will peak at about 9.5 billion between 2050 or 2060, and then begin to decline.
Clean water, land, food, they are all going to start costing more soon
In nominal terms, they will, but not as a proportion of people's total income. So they will cost more, but be more affordable. Resource consumption has increasingly become decoupled from economic growth, as technology improves efficiency.
If we could stop starting wars and cut the military we could easily afford it.
A more realistic option would be to fund space travel by selling ice cream made from unicorn milk.