If we get a universal basic income set equal to a living wage, then the "gig economy" can go back to being actual gigs, that is, people doing a bit extra to get a bit extra.
How many Americans are there (or just American adults)? 325M / 250M
What's those two figures multiplied together? 9.8T / 7.5T
What's the total federal tax revenues in 2016? 3.5T
To what multiple would we need to raise taxes to pay for such a program? Raise to 3.8x current taxation levels / raise to 3.1x current taxation levels.
All that assumes that basic prices wouldn't rise in an environment where money metaphorically fell like manna. (That $30K would have the same purchasing power as it does today, which seems unlikely.)
Adjust the assumptions as you like; IMO, there's no mathematically viable solution to a "living wage before the first hour of work".