It's built into the products I buy. But you're assuming that my supplier will lower his price to me if he no longer pays income tax. I say he won't. I know he won't if he's competing for my business with a foreign supplier.
You're wrong on both counts. The present tax may be "built in" but it is you who pays it.
His competitors will force him to lower his prices since their costs will also drop and they'd no doubt like to carve out a piece of his business for themselves if he doesn't respond. This applies whether its a US or offshore situation.