At this point I'd vote for the injector. Yank it and check it or better yet. If you can access it, make sure it doesn't test electrically open. The ECU maybe fireing it but if the coil is open it isn't gonna do doodley squat. That much at least saves you all of those O rings once you yank the fuel rails out. I know it's academic but I'm just cheap that way. If it's not electrically open and you think it's not putting out fuel, maybe one of those cleaner products that injects directly into the fuel rail can un clog it for you.
I really do hate paying what Toyota charges for those damn O rings. Gotta sit down and find another source some day.
The light just indicates that the ECU is firing the injector electrically and nothing else. The lack of the electrical impuse to fire the injector would be one of the more rare causes for an individual injector problem. It's kinda like testing to see if the wall socket is hot before fixing a lamp or applicance.
I guess the easy way get somekind of clue without pulling the fuel rail and the injector itself would be to pull the spark plug and see any fuel at all is making it into the cylinder. If it is, then you could try having them cleaned with the stuff I was talking about earlier. If not then I think you're gonna have to yank them out then clean and or replace as necessary.