This feels very much like a false dichotomy. Many millionaires, I assume we mean the extremely wealthy, have the majority of their wealth tied to the extreme growth of stocks based on some extreme economic forces. E.g. bezos with Amazon, Bill gates with Microsoft etc. And so some how comparing that to standard consumerism seems a little off.
Come on, that is basic supply and demand. The only confusing part is that inflation is often considered to be it's own independent thing and it can be controlled exclusively through e.g. the central bank when that's really not the case.
Consumer inflation = price of consumer good increases
Consumer deflation = price of consumer good decreases
demand exceeds supply = price of consumer good increases
supply exceeds demand = price of consumer good decreases
Now use these four basic definitions to answer your comment.
>Do prices for consumer goods rise when there are more consumers?
more consumers = more demand
UBI = less people work = supply stays the same or goes down
In this scenario "demand exceeds supply" is true. Prices do rise and that rise is called inflation.
>Do things rise in price when the people who usually buy the things have more money?
Again. UBI = less people work = supply stays the same or goes down
more money = more demand
People may buy more than one product if they can afford it or they may buy a higher quality one.
In this scenario "demand exceeds supply" is true again. Prices do rise and that rise is called inflation.
If you were to introduce price controls and set a maximum price for TVs then it is possible that one person buys 3 TVs and two other people can't get a TV at all. The answer is to raise the prices until everyone who wants a TV can get one.
>Are things more expensive in more populated areas or less?
Well, it depends on what "things" you are talking about.
A UBI does not influence the amount of land available so the supply of land would be fixed but the amount of money being received through UBI grows with a greater number of people.
supply = stays the same
demand = increases as more people live in a community
Therefore we see inflation in land prices.
If you were talking about something like an iPhone that can be manufactured in China and then shipped to New York then no, it would not cause inflation because denser populations do not prevent the Chinese (or any other company that's operating outside your city) from building bigger factories and thereby increasing supply to match demand.
supply = increases with demand
demand = increases as more people live in a community