With 6 different cars (3 Volvo, 1 Renault, 1 Saab, 1 Acura) each driven somewhat over 100K miles in my ownership (all bought used) I have replaced in total probably 4 wheel bearings, never more than 1 on one car. The most recent, a front bearing on my current 850, ran about $160 for the hub assembly complete along with about $125 for the work of putting it in (2 years ago). In every case the symptom was constant road noise, like driving on a gravel road. The noise gradually got worse (over a few hundred miles or so) until it became objectionable. If you raise the car you might feel some looseness on wiggling the affected wheel (assuming there isn't also a bad balljoint or strut mount).