The range of incomes I've seen from UBI proposals range from 10-20k/yr, with the high end generally applying to people with 2+ children. This is partially constrained by political reality, but politics aren't the only thing putting an implicit ceiling on the amount of UBI (as a reductio ad absurdum, consider why we wouldn't just give everyone $500k a year and all just retire onto our yachts).
Taking the midpoint, $15k pa means $1250/month, which means you'd need to make _$30/hr_ on software contracts to match UBI. You don't think it's plausible to fill the pipe with a 10-hr week of contracts over $30? Bear in mind that this means you'd need 3 hours a week or _12 hours a month_ with a more realistic (yet still quite conservative) income estimate of $100/hr, and that the type of person who's currently maintaining an OSS project is already increasing the quality of the talent/income potential distribution.
