The car runs rough. I have a P301 error and suspect the fuel injector, Yes???

What is your question?

I have changed the sparkplugs and swapped the coils and the same error appears, so it is not the spark plugs and not the coil. I have put injector cleaner in the fuel and run about 1/2 a tank, still no improvement. The check engine light comes on and goes off, and sometimes it blinks and sometimes it stays on continuously. If it is a fuel injector who can I get to replace it at a reasonable cost?