Here's the problem with going to Autozone. No diagnosis. Misfire cost? Well, it depends on what's wrong. We have no idea.
Have you pulled the plugs? What do they look like? Pay special attention to 1 and 4.
The good thing is that you have narrowed down a little. I would suspect something wrong in the ignition somewhere. This is where it gets tricky. You could spend tons just throwing parts in until the problem is resolved. Or, you can properly figure the problem out. Some things it might be:
Wiring Harness. (W140 too for the M104?)
Have you checked the connections? It might as simple as that.
I don't have much knowledge of the M104, but aren't there three coils? Would 1 and 4 share a coil?