This is a huge point, people debating UBI are often talking about different numbers. 1000/mo is probably too high, 400/mo is probably a better level and you're right its hard to live on that in a big city, you'd have to move out.
I think you're right that most people are talking about different levels. What frustrates me often is that when a UBI is discussed, very rarely do amounts seem to be discussed; whether in terms of montly payments, or overall cost of implementing such a system.
In terms of £400 a month. I think that is feasible (although still a very large amount of money!).
Although £400 isn't enough to live on, at all (I'm not sure if that's what you mean in your reply, or whether you're talking about 1000/mo?). It could still have other benefits - reducing poverty, allowing for extra leisure time, more risk taking in terms of setting up businesses etc.
I'd be much more open to a lower level of UBI than something that is "enough to live on without working". I think any large UBI just becomes incredibly difficult to fund.
