As a share of the USA's Gross Domestic Product, health spending accounted for 17.5 percent. Single payer systems like Canada are 10.9% and have similar or better health outcomes.

So, ~4.4% GDP is pure healthcare waste. Social Security is 4.9% GDP and welfare is another ~4%. So, right now we could use 13.3% GDP or 7k per person in the US. However, that 7k would remove the justification for a lot of low income tax breaks freeing up enough to hit the 1,000$ per month range without raising net taxes.

Now, this would take a huge shift at the federal and state levels, but compared to say the 'New Deal' it's not actually that large a change in policy. Further, while some people would stay at home, it would also free up a lot of jobs and inefficiency.

The real problem is a small but very influential slice of the population would be worse off.

PS: Remember, every policy change is going to make somebody worse off, so harming someone is not enough to make a change bad.

Not any more expensive than paying all the wages under the current system. Besides, it gets rid of the current welfare system's eligibility-determining bureaucracy, so it might even be cheaper.