If the UN is inefficient (which it is), perhaps we should try to work to improve. Dismantle it, and then having the create a new forum to discuss international matters would be even a greater waste of money.
The UN might nog be perfect, just as we humans continue to be flawed in most things we do. But they do have accomplishments (solved conflicts in Mozambique, Angola, etc.), helped fight diseases all over the world, preventing last year that ebola spread even further. Children rights are acknowledged, Improvement is maybe needed, but throwing everything overboard is to rash.
However, in 2017 (easiest year I could find data for), the US additionally gave almost $10 Billion in 'Voluntary' contribuitions, to support other efforts, such as WHO, ICJ, Peacekeeping, and other UN-related activities. That changes the per capita contribution to ~$31.6 per capita for US.
If we want to talk about areas where the US is shouldering an unfair burden, then military spending is the obvious elephant.
Never mind that the UN consists of a large number of agencies and thousands of programs that do all sorts of work, prepare agreements for intl. cooperation etc that ultimately bring lots of good to the world, eradicate diseases, provide refugee aid, facilitate air and sea transport and telecommunications etc etc that in many ways ultimately benefit also a farmer in Nebraska. Wars seem to be the most difficult to manage but that's pretty much a human fault, not limited to UN.
To give you an idea, for the year 2020, Overseas Contingency Operations were estimated to cost approximately $174 billion (that includes the war on terror, wars in Iraq, in Afghanistan).
Now, we can still debate how much the UN really is useful for maintaining world peace, but only a few that are delusional would argue that the US overseas military actions are doing a better job.
But I'll admit, even though it proves one's point, it is not only about military expenditures. If you have a look at the whole US federal budget, the amount that goes to the UN is negligible, a drop in the ocean.
Not to mention that the UN was never created to meet US interests. It is still not the case today, even if they are the biggest net contributor.
16/20 (80%) is better than only 1.1% of the rest of you guessers. Interesting.