This is where the income tax idea will be presented. Quick summary:

It appears that the State Legislature (or the City of Seattle, with Legislative support) could pass a flat income income tax with a standard deduction. A 1% income tax with a $1,000 standard deduction per household could raise in the ballpark of $138M annually (based on 2018 American Community Survey data). Under this regime, no Seattle household earning less than $100,000 would pay. The same extrapolation suggests $356M King-countywide, including Seattle, and $736M in total statewide.