If it was my car I would go ahead and replace the injectors and like most shops just throw parts at the car until its fixed, I would take the same aproach but do the work myself to make it cheaper..
Or I would pay out the butt for a diagnostic fee and get a technician to take a looksy also in an effort to save from overspending on parts. Just dont take it to a place thats just going to throw parts at the car because im sure you can do that yourself for alot cheaper.
However its not my car so what about any leaks? Any reason to beleave you have a possible blown head gasket thats causing the misfire? Does or has the car been burning oil at all? Its hard to figure out whats going on without being able to experience the issue and play with the car.