The rear wheel bearings in a 2003 Buick Rendezvous are integrated with the hub, therefore they are only available/replaceable as an entire hub assembly. The rear hub assembly costs around $200/each, depending on the specifics of the vehicle (2WD or 4WD).
Remove the tire and wheel from your 2003 Kia. Remove the axle end. Remove the wheel bearing retaining nut. Remove the wheel bearing and the wheel seal. Reverse the process to install the new wheel bearings.
The bearings are not replaceable, they are a part of the rear hub assembly - the studs and the bearings are pressed in - replace the whole hub assembly - 4 bolts are holding it. Rear bearing/hub bolts (new only) are to to be torqued to spec. [2000 Montana - 85 Nm (63 lb ft)]