[Principled]

Uh, the flat tax uses income minus savings as a base. It's subtracted from this base. It doesn't "add" to prices.

Irrespective of base calculation, the flat tax does indeed add to prices. Remember the taxes and tax costs (for the flat tax, that would include employer "contribution" payroll taxes)? Those costs are added to prices, subtracted from wages, or removed from ROI.

[Your Nightmare]

Irrespective of base calculation, the flat tax does indeed add to prices. Remember the taxes and tax costs (for the flat tax, that would include employer "contribution" payroll taxes)? Those costs are added to prices, subtracted from wages, or removed from ROI.

May be added to prices, and if those taxes are added to prices, they most certainly aren't fully. You need to read up on tax incidence.