Hmm... I think there's a few things to take apart.

First, the implication that "everyone could have a no-strings, no restraints right to the basics of life on their own terms"... That's not an implication. We even know what it would cost. And it's a lot less than a UBI would cost. But not if we decide to gut EVERY social program for a half-ass UBI.

And as to "living in the most expensive..." Most people don't move. One of the common things that come out of UBI discussions is that many UBI advocates are more than happy with forcing people to move 1000 miles away from their family. I am not.

But I also think you misunderstand what an "expensive city" is. Largely, regional pricing has to do with the value of the dollar. Poor people in New Bedford making $15/hr are still living the same life with the same buying power as someone in Mississippi making $7.25/hr. They're not there because of food, views, luxuries. They're there because their family has lived there for 50-100 years or more. Or, making a bit more, they might be there because they work a regional trade like fishing. I don't know of any big fisheries in Mississippi. You talked like living in an "one of the most expensive cities in the world" is a luxury, but instead it's the same as comparing Mississippi to San Miguel Island. It's basically just a currency exchange thing.

Speaking of that... Yes, we should be normalizing the value of a dollar across the country. It's wasteful that it's cheaper to live in a mansion in the desert with all your resources imported from abroad. But it serves society better to finance someone living in New York than make them move to somewhere like Arizona because it's cheaper. So we should be solving that problem, not passing yet another "tax break for the rich".

But let's look at "concentration of funds should be allocated there ". This is the big one to me. Who do you think is PROVIDING those funds? All of them? The same locations in question are "net taxed". We already contribute more than we receive by a large margin. You're suggesting we should make people move to net-receiver states for UBI, but look at what that means. It means a cash waterfall from the poor net-provider states to the non-poor net-receiver states. Do you really think anyone on the Left should be ok with the poorest people in the country paying for people in random non-poor states to live like kings? I don't think "ok, leave everything and everyone you know and move to a deeply racist state so you can live better" is reasonable.

Because there are clear reasons why a person might prefer to live in one place rather than another

Absolutely. But I will point to the desert states. The environmentalist in me is against rewarding people for living in locations with massive carbon requirements just because "my UBI will let me live rich". In fact, ANY mass-exodus and breaking-up of families is a con for UBI for me.

why people being stuck in Mississippi in a housing welfare scheme with some lock in would be getting screwed over compared to people lucky enough to have started off in Boston

With all due respect, you seem to be confusing the current cost of living with some luxury. Other than the local government being shit, there's nothing wrong with Mississippi. And if my family weren't here, I'd be fine living there. I could sell my crappy house 3 hours from Boston and buy (checks zillow) an 8bd 5ba on 15 acres 1hr out of jackson and no longer have a mortgage because of the price difference. It's not that my area is rich, it's that the dollar is weaker. You talk like living in or around Boston is some kind of blessing, but the actual poor people in the US are STUCK here. And $1000/mo won't get them unstuck. And as a reminder, Massachusetts needs less federal funding because it takes care of its own, so the UBI would be paid for by the taxes of poor and middle-class people STUCK in states like Massachusetts.

And it isn’t really possible with zero lock-in or barrier to entry either, because of the previously mentioned finite nature of housing availability vs demand

I think you're accidentally arguing my side, now. If you can agree that the clear majority of poor people live in high-cost areas, and you are raising the point that people cannot move, then doesn't that end the discussion? All of your arguments I replied to above involved either "well they can just move" or some explanation that you think someone is luckier to be on food stamps in Boston (...than what? Since they're less likely to need food stamps in other states).

But something like national Section 8 would absolutely give more freedom and less barrier of entry than a UBI. And there's PLENTY of housing availability everywhere. Especially considering it would never turn into "everyone is moving to Boston at once". People don't want to move to Boston like that. But also (and I say this as a country boy), it uses less actual resources to support people in cities like Boston than in the country. That's just simple logistics.