cost,fuel injector replace.300zx ,six cylinder

Depends. new injectors are around 150 each, plus o-rings, plus labor. most shops charge around 6-8 hours to do the job. depending on their labor rate it can get quite expensive. I normally charge 1500 parts and labor for all 6, which is the recommended repair. you can choose to replace just 1, but they usually fail one after another.