They are about $10.00 from any auto parts store. As for putting them in, it can be a pain, but once you do it once from that point on they get easier. I had one put in at a shop, while on vacation and it cost between $75 and $90.00 I think.
But if you decide to take on the task yourself, make sure you read up, because it's easy to screw up the bearings in the new one if you are unsure.