Depending where you live 'enough to live on' will vary. I lived on about $700 / month pretty happily for 4 years in college. Doesn't need to be a desirable long term amount but it does need to solve the problem of the unemployment trade off, namely that if you're getting unemployment and you get a job you lose it. A BI needs to simply ensure that you have a base level and if you get some work, you make more money...period.
