My 1990 300zx has one bad fuel injector. I would like to replace all but cannot afford 6 nissan original part injectors. Is replacing w/aftermarket injector recommended? If so which one?.

No, this does NOT mean all the injectors are gone. 1990 vehicle 26 years old but cycle time on injectors is 90,000 miles Theoretically, they can cycle for 370,000 miles or 25 years, (arguably) or more... OK most issues are do to pintle becoming clogged or partially blocked the effect causing a poor spray pattern and reducing the atomization and efficiency.