242 million adults in the US.
Just $10,000 per adult is $2.4 trillion. That of course wouldn't come close to being enough. Even if you assume tax redistribution of the money (rich people getting UBI, and then having it taxed away), for $2.4 trillion you probably would only manage to get the poorest 1/4 up to something like $15,000. Today the poorest 1/4 are receiving a net of more than twice that sum between Federal and State benefits.
Federal budget ($3.9 to $4.1 trillion or so depending on which year we're talking about) minus dozens of things that won't be replaced by UBI and won't go away (eg NASA, military, agriculture subsidies, budgets for countless agencies like HSA or FBI, transportation, justice and so on) = you might be lucky to break even or bleed just a few hundred billion on the budget if you allocate $2.4 trillion to UBI. That's assuming Social Security, all housing subsidy programs, all welfare programs, half of all social services programs, Medicare, Medicaid, Obamacare etc etc are all ended.
The equation at the state level is a whole 'nother calculation, and would be a very significant factor given the states budget is another ~$1.7 trillion and represents all sorts of welfare programs and healthcare spending.
Personally I favor Warren Buffett's premise of significantly boosting the earned income tax credit, and freezing or lowering the minimum wage. The UBI is dramatically regressive, there's no reason to be giving the top 50% in the US a UBI.