Millage rate determines your property tax. Some counties reassess them annually. Unfortunately I live in one of those:>) It is based on average taxable values which of course move with the market. Pull up the tax assessors site for the county you plan to move to. You can either use tax tables if they are posted or simply call.
We are looking at moving to TX - average for 400k is 12k annual tax in the county we have to move to.