You forget that with real UBI funded by progressive taxation, people past a certain point pay more into the system that they get from it. So in practice, not everybody actually gets $2000 more every month relative to their current income. I would suggest taking IRS numbers for various income tax brackets, putting them into Excel, and playing with the numbers to see just how progressive you need to make the tax to make sure that nobody gets less than minimum wage, for starters. I'd share my spreadsheet if I still have that around.
The bureaucracy to manage such a program is orders of magnitude less than for any other welfare program, because it's not means-tested. In fact, since IRS already has the bureaucracy and the logistics to handle tax returns, there's no reason why this couldn't be tacked onto that.
As I've laid out... you gotta come up with $3+ Trillion more every year... at a bare minimum. The real numbers probably look closer to $4-5 Trillion if the plan is to give everyone over 18 this $2,000 monthly, plus you have all this Bureaucracy you'll need to manage this program. You gotta double the national budget and then some.
There are no numbers that make sense to pull that off. It's a fantasy to think otherwise.