Canada

This assumes that people wouldn't take the same job for less pay if they were guaranteed a fixed amount that more or less made up the difference. If I work a job where I make $50,000/year, and I went to a world where I made $20,000/year UBI and $30,000/ year from my job, I could end up ahead under this scheme with the only additional cost to the economy being my possibly lowered taxes. Under this plan, raising taxes and lowering minimum wage/wage expectations means there would be at most a slight change to corporate taxes (and some jobs would have to pay more when you factor in UBI because desperation would be less of a factor for what people are willing to put up with).

So, realistically, the only cost would be whatever is required to get whoever is below the set line up to the set line, for individuals, corporations, and the government. This would also depend on people who are already making more than UBI to take a "pay cut", and for corporations to not resist paying more taxes to balance the lower payroll costs. So it's never really going to happen.