$15? $25? $0 because the children yearn for the mines?
It should be tied to the highest COL region (so that it does not economically limit geographic mobility) and it should allow someone living there to:
- Pay rent of a 1b/1ba apartment at current market rate with less than 1/3 income. As well as utilities (Internet included)
- Pay for a healthy diet at current costs of food.
- Pay for all medical care that could be necessary (this shouldn't actually cost anything but a small tax on the income).
And
- Pay for tuition and all costs associated with being a full-time university student while working 25% of the year. Or
- Leave sufficient income after expenses to save up for a market rate home in 5-7 years of working full-time.
(Note that this is all predicated on continued use of a capitalist economic system and would likely be much easier to achieve in ways not directly tied to wage in a more advanced economic system.)