obviously if it sounds like a WRX then one or more of the cylinders arent firing.
Possible causes...dead sprak plug from pinging, old age, over fuelling etc, coil pack dead....swap for another one, or closed injector (probably not)
Dont ever waste your time at these nuffy chain mechanics. If you cant do the job yourself then im sure some good friend off the forums can come around and have a look for you. THen if it stumps the more seasoned backyard mechanics then take it to the reputable big guys who wont spin some crap.
FYI, yes there is a cam sensor. It sits on the end of your exhaust cam and looks like a cup face down. If thats the problem then the car might start to compressor surge, will drive ok, then suddenly have flat spots or just generally be impossible to drive. I wouldnt think that would be the problem in a 34.
If it is then theyre available a lot cheaper than that second hand, all though that price he gave you is pretty much spot on from Nissan.