As discussed above, funding for UBI can be mostly reassigned from existing welfare & pension budgets.

Demand for basic food and shelter is more or less a constant (unless you can argue otherwise), regardless of people's income, so as I see, prices for non-luxurious items could stay about the same under UBI.

It's a simplistic overview and there are tons of important factors e.g. farming subsidies or migrations, but in general UBI makes a lot of sense.