That's not how any of this works. You're assuming that every single person will spend their UBI payment in exactly the same fashion, and thus that all prices will go up in unison. That is an extremely basic model of the economy (i.e. it's not a good model). It doesn't take into account people saving, people paying off debt (another form of savings), or any sort of second-order effects (how will this effect how people operate in the labor market if they know they can leave a crappy job and not become homeless)?

"First order thinking" is not a euphemism for "I'm right because I said so".