Hi Scatz - yeh I hate to throw money at a problem just to find out its something entirely different.
Maybe we can work together and figure something out - let's review the situation.
1. Does the engine misfire all the time or only at idle
2. Is it worse when cold or warm
3. Does the engine start easily
4. Any signs of backfire via the inlet manifold or exhaust.
5. Any warning lights on the dash
6. Have you checked all the plugs to see if they are all the same colour
7. Any hissing sounds when ticking over
8. Does the engine sound like it misfiring when idling or haunting
9. Is the engine using any water
Yeh a load of questions but it may help us rdeuce the possibilities