Again, in some places this might happen, but not everywhere. For example, do you really think that it won't be possible to rent a room for less than $10k/year ($813 per month),
anywhere in the country?
Secondly, if your net income is currently $0, then it's hard to imagine that price inflation alone could be enough to keep your purchasing power from significantly increasing with UBI.
Thirdly, labor supply might not necessarily be removed; there would be less need for a minimum wage, and fewer cases where eg. disability payments or unemployment payments are an active disincentive against working (get a job and get paid less than you earn on unemployment handouts), so there's a reasonable chance the labor supply would increase for many tasks.