unless you actually used a torque wrench, how do you know what the torque value is? You haven't said which side rear nut nut either. The left rear can come loose due to wheel direction in rotation is opposite to the tightening direction.
The ONLY way to know if the bearing is damaged is to remove it (which destroys the bearing) and inspect the surfaces for wear and pitting.
I highly doubt your weight plus the 3' bar overtorqued the nut. In my mind the bearing is still suspicious however. If it was loose and you DE'd the car that way, the aluminum trailing arm and the steel bearing could be at issue. BTW the quote is off the charts in my book. Search on the forum here for the home made wheel bearing puller... about 20 bucks of pipe fittings and a bolt should get you sorted out. Put the new bearing in the freezer overnight. When you insert it into the trailing arm, face it with some antisieze and tap the edge to start it and use the puller to put it in the rest of the way. Head to the track. If you don't remove the trailing arm there is no need to realign or corner balance.
edit; here is the thread:
Rear Wheel bearing replacment