189k on a 300zx isnt much if it has been taken care of.

-clunk in rear end could be loose/worn bushings (motor mount, tranny mount, driveshaft center bearing, differential bushings)

-Shifter vibration could be the shifter bushings which are like $2

-Engine ticking could be the common lifter tick which could be cleared out with an engine flush. If it is a LOUD tick it could be rod knock which i wouldnt mess with unless you want to do a rebuild

i would pay around 2-3 grand depending on the body and interior also