As a small business owner in a non sales tax state, I can tell you that a national sales tax is the worst idea imagineable.
Income tax is based on business records I keep anyway. A sales tax requires that I keep additional records and proofs in addition to those I keep in order to become a tax collector for the government.
Prices will not go down. This is an economy killer.
I am definitely in favor of a Flat Tax proposal of 5%-10% and making the first $30K non taxable (per wage earner, not per household) and an additional $10K per child so a single mother with 5 kids could earn 80K untaxed.
Call me crazy, but I think you'd see a business and a marriage boom, even in the inner cities.