You may not be able to put a price on the human spirit, but NASA's contractors sure enough can put a price on space exploration. As firecracker said, there are always choices to be made. We have to choose how much we spend on domestic causes, on war and defense, on the space program, or on any other program funded with public tax money.
I'm not against continued space exploration; I just think that no more of the budget should be spent on it than at current... if anything, the percentage should go down, given the rather extraordinary defense spending and tax cuts of the current administration.
Manned space flight is several orders of magnitude more expensive than unmanned. Why do we need to land people on the moon again? We've already done that....quite a few times. Why not push the limits of unmanned space exploration? Why not try to keep travelling farther and more often and at less cost, at least for now?