Yeah, as I said in my comment, the primary way to pay for it is to adjust marginal rates so that it's (mostly) a transfer from rich to poor. If you're rich, you'll get a $1k UBI and also pay $2k more in taxes (or $4k, or whatever). Probably for those at the median income it would be roughly neutral - but with the benefit that if you ever lose your job, or want to leave an abusive marriage, or want to try starting a business, you still have that $1k coming in.

Medicaid and Medicare being wholly replaced by a truly universal plan unrelated to UBI is probably a prerequisite for a UBI for a bunch of reasons. Social security would probably be unaffected, at least initially, and SSI/disability would likely either be reduced or gradually phased out, depending on the amounts.

I know the other various benefits aren't huge in the budget, but they add significant bureaucratic burden to both the state and the individual. Eliminating that would be a big benefit of UBI.