$12k is the cited number that you see a lot in basic income discussions. That's just over the poverty level. That's not enough to live on and it's practically a bonus for some members of this site. It's not enough to do anything with.
But just to do that in the US you are talking about 3 trillion dollars (300 million x $10k for easy math) that you have to find in the budget. Now basic income advocates will say you can make up some if not most of that by cutting welfare programs, but given the nature of welfare programs - good luck. That stipend is also not enough to pay for healthcare, so you can't cut that.
How exactly do you convince a nation which already isn't willing to pay for healthcare to pay for basic income, too?
I'd love to be wrong, but I've never seen any numbers that are workable, especially in a political climate anything like today.