I would replace them in a pair as if 1 is gone then other my be not fair away.
I did the front bearings on my cg lancer and I think the bearings are around 100 each(rear could be cheaper). then if you going to pull the car apart your self will make install cheaper, and you need someone to press the bearing in.
I think mine cost me somewhere between 300 and 600 for the whole job but that was a few years ago.