So ignoring Medicare / Medicaid / health insurance in general, the current expenditures on social security / unemployment / welfare add up to ~$1.4 trillion, which (given the 235 million adults stated in the article) is ~$500/month per citizen.

I could easily live alone on that in parts of the country. Given that people surviving on said basic income could (and should!) have roommates or spouses, it's even more than necessary.