> Every single proposed UBI was either insufficient to cover people's basic needs, obscenely expensive, or both.

I don't think that's true. In a really simple model imagine UBI of $2000/month given for everyone. Then imagine increasing income taxes by $2000 for all employed workers. Then the true cost would be difference between current unemployed benefits of the UBI, which shoudln't be obscenely expensive (in normal economic times). Employed workers shouldn't care about the increased taxes because their take home money would remain identical.

That's of course a very simplistic model, but explains how you shouldn't just count the UBI amount times population as the cost.