UBI is generally not metered by "%" but some flat quantity of money, whether nominal or real. That is, like a "head tax," but...negative.

In that common formulation, it would compress consumption by the entire tax+benefit base, that is, everyone would move towards median consumption by some amount, keyed to the magnitude of the UBI, if funded by any kind of proportional taxation (including a nominally regressive proportional tax, like consumption tax/VAT).

Politically, it has tough problems: 18% of the population [over age 65] already has a "MeBI" in the form of Social Security that they can vote to increase, and 22% of the population is below the age of 18, and can't vote. So that's 40% right there. Of the remaining 60% in their working years that produce the output split among themselves and that 40%, quite a few would rather not be compressed towards median consumption: the voting population is shifted higher in the consumption deciles, and people are not often so disposed to think they might find themselves luckless in the future. There's a thicket of "tax expenditures" that can form a "MeBI" for the electorate at the upper-half, like the mortgage interest deduction.

If we look at the difficulty in gaining electoral support in splitting consumption to the benefit of minors (thus, future labor) to even things out a bit, in the form of the semi-recently expired expanded child tax credit, we see the magnitude of the political problem.

Personally, I prefer to see UBI as tax reform to avoid crazy wiggling in effective marginal tax rate. But there are many reasons why it's unlikely that the electorate would see it that way, or approve of it even if they did.

> Also UBI is funded by taxes

Some of those taxes are already being paid. We have a lot of social programs that, for what could politely be called "political reasons", include extensive administration whose primary function is gatekeeping and means testing. Often, the administration of those programs costs substantially more than any money "saved", leaving aside that it also has a very high false positive rate, excluding people who actually should have received it. But there is a political faction that would rather see government burn a billion dollars just to make sure a tiny fraction of that isn't paid to someone who didn't "deserve" it. To quote https://www.bitsaboutmoney.com/archive/optimal-amount-of-fra... , "the policy choices available to them impact the user experience of fraudsters and legitimate users alike. They want to choose policies which balance the tradeoff of lowering fraud against the ease for legitimate users to transact."

Eliminating entire programs and the massive administrative overhead of those programs, and replacing them with something that merits the label "universal", is much more efficient.

Also:

> on a nationwide scale it means everyone got x% more money and the market would adjust itself accordingly by raising prices?

This is assuming the injected money has zero multiplicative effect on the economy, which is very unlikely to be the case. By way of example, since we're on a site created by a startup accelerator: Many, many people have said that UBI would be a massive boon to the startup ecosystem, by making it possible for many more people to safely try to build a startup without as much personal risk.

Analyses vary, but some analyses have suggested that UBI may be a net benefit to the economy. At the very least, economic boosts provided by UBI substantially offset its cost. That's in addition to the offset mentioned above of replacing existing less-efficient programs with UBI.

> improved an ACA, a cap on healthcare costs for all if you will and free yearly health checkups.

We should do this as well, because healthcare is one of the few things that isn't addressed by UBI (since ultimately it's an insurance mechanism).