The 2022 budget was $1.2T across all welfare programs[0]. This includes programs people don't normally consider welfare such as the Child Tax Credit and parts of the Pell Grant.
There are currently 350M people in the USA [1]. $1.2T / 350M People is $3,428/person/year. Please note that while significantly less, there will still be some overhead in the UBI program so the actual number is lower.
This also doesn't include state budgets for welfare.
[0] https://budget.house.gov/press-release/7582
[1] https://www.worldometers.info/world-population/us-population...
If we raided these programs, along with the previously mentioned programs, we reach an annual budget of $3.5T. The per person math is $10,000/person/year. A two person household would very near the federal poverty line.[2]
It's starting to look like it could be viable if we add state budgets into the mix, and find another solution for elderly healthcare.
[0] https://www.cbpp.org/research/policy-basics-where-do-our-fed...
[1] https://www.cms.gov/data-research/statistics-trends-and-repo...
[2] https://aspe.hhs.gov/topics/poverty-economic-mobility/povert...
It's really just UBI advocates handwaving away the question of funding.
There will, of course, be people who consider this to be a feature, not a bug. That's an ideological difference outside the scope of this comment.
[0] Source: I know someone applying for long-term disability. Getting an answer to a question as straightforward as how to sign the paperwork (wet signature, digital, print/sign/scan, fax?!) has been a challenge for them. It's also unclear if the three different signatures needed of them are even to be done the same way. This is a generally competent, functional person I'm talking about, by the way.
Edit: I'm failing to find numbers to support this now.