Every person can just go to a special Costco like store and spend x credits a month taking whatever they want. That way we can just make that stuff as efficiently as possible, rather than messing with the whole economy.
The IRS sent me a $1200 months ago via direct deposit in the bank account it already had on record for me. Setting up public bank accounts at post offices so every citizen has access and having the tax apparatus that already collects all your financial information reverse the process for 12-24k a year is extremely easy to implement compared to establishing entirely new branches of government.
There might be an argument that the food stamps program can be made universal for a fixed amount for everyone as a compromise position. IE you get 800 instead of 1k a month in UBI but get $200 on an EBT card to buy food with. But a UBI lets you simply abolish the bureaucracy of food stamps altogether.
It might be harder than just handing out cash, but it would be significantly cheaper, and could be implemented in small steps.
Staff and fund it properly. Have a good corruption watchdog. Run government departments against each other with bonuses for "the winners".
Fix government, don't dismantle it.
Compare that to US defense spending now. Of course, 2.4 trillion a year in UBI payments is still 4x more than the US spends in the defense budget every year, but defense is a monetary black hole - the return on investment is awful because unless all the personnel and equipment commitments correlate directly to substantial amounts of economic enablement (and they really don't - the most direct example is exposing oil markets in the Middle East through occupation in recent years, but pretty much no country on Earth is lining up to pay what would functionally be protection money to the US military mob for being global police) then you build the tanks, bombs, trani the troops, run the bases, etc to do the equivalent of dig and fill ditches. There is no realized productive value in having the weapons capacity or entrenchment internationally the US military has.
That is the kind of money drain in government that can wreck a nation through siphoning of its profitable yields. Most would spend UBI on immediate goods requisite to human survival, that is a huge capitalization opportunity. Tremendous growth. The rest would be paying more in taxes than they get in UBI anyway to cover the costs.
The point I was trying to make is that you don't have to upend the entire economy to help people in need.