2004 350z
 

Test drove the Z, the gear shift was very noticeably shaking while stopped. When first taking off in gear, the engine sound normal, then it got LOUD and kind of a wup wup wup noise, almost like a loud fan, worth buying or fix going to be terribly expensive?

with your vague crappy explanation, not to mention nobody can tell you from behind a keyboard what is wrong with it.

pay to get it checked out

yes

Nah, the engine's done. The wups are too short.

Could be anything from a crack in the exhaust pipe (inexpensive to repair) to a warped valves (very expensive to repair).