That likely depends on the individual proponent of UBI. From what I hear in Germany, it's supposed to be higher than our current from of welfare, which puts it somewhere at ~1000 Euros a months at minimum, so you can cover an average sized apartment, subsidized health insurance, utilities etc.

I know people who live -in their eyes- comfortably off of that. They see no reason to change anything, as enough is provided to eat, sleep, smoke, get drunk, have a TV and an xbox, a computer and internet and use public transportation to meet with friends. Sure, you can't easily travel, and you're not going to buy a house any time soon (but if you own one already, you can keep it; if you're still paying the mortgage, the state will cover it for you within reasonable limits), but it's a comfortable life if you don't have a lot of ambition or can make some money on the side.