The number I’ve heard floated is $1,000/mo per household. There’s ~118M households in the US. That’s $1.4T/yr. Tax revenue is $3.2T, so we’d spend 44% of revenue on it. Unless you’re rolling social security and medicare into it while telling old people they have to buy their own healthcare, then it’s not even close to feasible.
Social security - $910B
Medicare - $588B
Medicaid - $368B
Interest on Debt - $241B
If you left those programs unchanged, then you’d have $3.5T of spending on just those 4 things and UBI. There’d be zero money left.