I support basic income in theory, but it's definitely an expensive proposition (for which reason I don't think it will be viable for several decades). Let's say the average American adult needs $15,000 a year to live on frugally. (This is almost exactly the amount of money you make from working minimum wage for 40 hours a week every week of the year. Frugally is the key word here- it's perfectly reasonable to live on $15,000 a year in Arkansas or Mississippi, but not SoCal or the NYC metro area. It's very difficult to live on minimum wage in practice because very few people on minimum wage work 40 hours a week of it. We can also assume universal healthcare, because "can reasonably live on [frugal income]" should be possible, but isn't without universal healthcaren) You could even cut this down to eleven or twelve thousand dollars on the assumption that even people who live mostly on the basic income payout will also be holding down a part-time job to supplement it. That might not be much- especially since we won't need a minimum wage anymore- but it be less than five or six thousand dollars a year. Children would get a smaller payout, but nothing less than probably around $7500.
As of this writing, there are 317.5 million people in the United States. 23.5% (74,612,500) of them are under 18.
Under a generous basic income plan, where adults get $15k a year and kids get, let's say, $9k, minimum income would cost 4.3 trillion dollars every year. Under a cheaper plan, where adults get $12k and kids get $7.5k, that's still over 3.4 trillion dollars a year. The former is more than the entire federal budget (3.9 trillion). The latter is under it, but not by much.
It's probably a lot more viable than it looks, since we wouldn't also be spending money on Social Security or food stamps, and business taxes can rise since there's no minimum wage to worry about, or a lower one- but it's not cheap. I don't have the stats in front of me to do the math right now, though, since I have work to do. What I can tell you is that we can't make the shortfall up by cutting from the military budget- that's under $700 billion/year.