The total cost of this experiment may be a lot less than you expect. I'd encourage you to make a guess as to what you think it could cost the US taxpayer and then check what the Department of Energy contributed [1].

The LZ collaboration is going to run their machine until at least 2030. They have almost no hope of making a meaningfully larger detector, no will you hear them suggest one. Their detector is already designed at such a scale that it contains a substantial fraction of all the needed xenon isotope available on Earth.

[1] https://news.wisc.edu/dark-matter-detection-receives-10-ton-...