There are different ways to do the accounting here. The opponents like to just add up the sum of everyone's UBI and call that the cost. But if someone pays $12,000 to fund the UBI and then receives a $10,000 UBI, the net cost to them is obviously $2000 rather than $12,000.
Calculating the overall net cost is also not very useful, because it's effectively zero outside of some minimal administrative costs -- payments in equal payments out.
Probably the sensible way to do it is to calculate the net loss to people who pay more than they receive, e.g. $2000 to someone who pays $12,000 and receives $10,000 but $0 (rather than -$2000) for someone who pays $8000 and receives $10,000.
Using those numbers you end up somewhere in the ballpark of 25% of the cost calculated using the first method, because you take the total cost and subtract out the UBI the top half of the population is paying themselves, and then half the remainder for the bottom half, because people in the bottom half would be net recipients but would still on average be paying half as much as they receive.
Whether this is exactly 25% depends on the income distribution within the population. It gets higher the more inequality there is. If everyone had exactly the same income it would be 0%. If there is great inequality it would be higher, i.e. more dollars transferred from richer to poorer. But that's kind of what you want.
The most important factor in the cost is obviously the amount of the UBI. It can be made arbitrarily more or less expensive by changing that.
> I would be more in favor of a jobs guarantee since I think people find working meaningful
There are reasons to think that would be a bad idea, e.g.:
http://slatestarcodex.com/2018/05/16/basic-income-not-basic-...
Moreover, half the point of a UBI is that it doesn't impose costs on working, unlike means-tested programs where earning money from working causes the loss of benefits.
It's one of the things that allow it to operate productively even at below-subsistence payment levels. The highest paying job you're qualified to do may not pay enough to subsist on but becomes enough when combined with a modest UBI.
And for someone who genuinely can't find full-time work, they're more likely to find meaning -- or a lead on gainful employment -- by volunteering somewhere of their choosing rather than being forced to dig holes and fill them back in with insufficient free time to improve themselves and get out of that situation.