The clunk that you describe is most likely failed rear subframe bushings. Which at that mileage, you can absolutely assume are completely trashed.

The good news is that you can do the subframe bushings on the car with almost no disassembly in an hour (if you work fast), or two (if you're slow). This does require the special tool.

If you are on a time and money budget, the bang for buck items are:
front thrust arms
rear subframe bushings.
front control arms

I would try to do more than that, but that's the absolute minimum.

__________________
2011 M3
2006 Sierra 2500HD 4WD LBZ/Allison
2004 X5 3.0i 6MT
1995 M3 S50B32
1990 325is
1989 M3 S54B32

Hers:
1989 325iX
1996 911 Turbo