A few solutions: 1)Have the government set prices for basic necessities. 2)The government owns companies that produce basic necessities. 3)Replace capitalism.
All the solutions above have its drawbacks.
You think people are just going to accept starvation? Shit will get real, real fast.
And most people aren't as articulate or reasonable as the people on this site.
There will be massive violence.
A better way to look at UBI is that it's not about giving poor people money. Its about keeping the fabric of society together and preventing revolutions once automation hits fully.
With 100% robot labor, utilization of a resource is purely a political decision. The idea that we should give outsize rewards to historical incumbents for their historical incumbency becomes sort of silly.
There is a cycle and how quickly it cycles will be determined by how quick the various parts move. Not all robot owners will increase their prices just as fast and people will not buy from the overtly expensive sellers. Similar to the economic cycle we already have.
I certainly don't have an economics degree though.
It's very expensive to develop a machine that can replace sewing workers (DARPA is working on one because the US military has a need for it). It hasn't yet created any value because fabric is ridiculously complicated for robots but comparatively very easy for humans to manipulate). So far, the sewing robot is neither very useful nor very valuable (since it is still orders of magnitudes more expensive than fabric workers).
If low-paying work is less desirable than it is now, companies will have to deal with the game theory reactions of how consumers react to there being a shortage of fast food workers, bus boys, valets, etc. There is a certain amount of slack that consumers will absorb, either in resources (time, money, effort) expended. IKEA makes you bus your own tables like a cafeteria. I imagine if bus boys and fast food workers suddenly became more rare / expensive, companies would ask their customers to inconvenience themselves to maintain their profit margins / economic viability.
Why not just decrease number of working hours to say 2 per day, but for everybody, instead?
Maybe you would, but I think most people would rather have a job and be fabulously wealthy relative to those surviving on UBI alone. See: all the people who work 60h a week in SF making $200k instead of chilling at a bank working 35h for $80k.
It's not a joke: post-USSR countries already have exactly this problem.