Its not really about cost.
It's just political manouvering and maybe the undercurrent of anti-science that pervades the US at the moment.
People always mention how expensive Apollo was but it wasnt. I bet at the end the Apollo project ended up making money and the US still reaps many financial benefits today from it.
All that govt money created thousands of jobs, hundreds of businesses, marketable patents and products, science programs, scholarships, blah blah blah. Fantastic stuff, never has such value for public money been given.
Inverstment in space and science makes money.
Nowadays here in the UK we dont bat an eyelid at pissing half a billion on empty 999 centres or 11Bn quid on another NHS nothing project.
Priorities skewed perhaps?