Keep in mind that when you are counting per person that means you are allocating that much for people not in the workforce like children too. A 4 person household is getting $50,000/year with the above number.
Expecting people who are just living on a UBI to move somewhere with a low cost of living also seems reasonable to me, I suspect you could substantially slash even the $12,000/person/year number and still have it be sufficient.
I also think that a partial UBI (e.g. $3000/year) would likely be nearly as beneficial as a full one, but it does increase overhead costs because then you can't get rid of the rest of the social services.
(Other people have addressed the fact that a comparison to GDP isn't valid because of taxes).
> not counting in any overhead / administrative costs to give out the handouts.
These costs are negative, in the sense that it allows us to remove the other low income services with much greater overhead.