At $1500/mo for everyone in the US, that comes to just shy of 6 trillion USD. For comparison, the total federal tax revenues for 2016 are going to be approximately 3.5 trillion USD, including payroll taxes.
At $1500/mo/person, this one program would present 5/3rds of all federal tax revenues.
A more realistic figure is probably much closer to $650/mo, assuming you take ALL of the current federal spending on healthcare, social security, veteran's benefits, pensions, and welfare and direct it into UBI. This says nothing of the legality of cancelling existing or contractually promised federal pensions, nor the morality/practicality of changing the existing social security and Medicare systems, of course.
$650/mo/person still leaves us with a deficit (as today) and is a pretty meager existence for sure!