Kill all federal funding to cities and states.
Sounds good, until the people who live and/or work in those cities stop paying the tax money that provides that federal funding. And make no mistake, there are quite a few corporations in those cities that provide a lot of income for the IRS, especially when you factor in what their employees are paid.
Better to stop the frivolous funding across the board, and not just the sanctuary city nonsense. i'd start with the federal funding that is provided to the ACLU, then PBS, then National Endowment for the Arts, and then ALL foreign aid, and then...you get the idea.