I always replace the whole axle since it doesn't involve any more labor. And, think of it this way, if conditions were right to make one joint fail, the other's not far behind. Expect to pay about $100 USD for a rebuilt axle.

I get my axles from http://www.raxles.com/. I've actually met Marty and toured the facility. It's all top notch.

I don't know for sure if it helps anything, but I always hit the CV boots and the steering rack boot with Armor All when I change the engine oil. Joints wear out b/c the boot gets brittle and tears-- allowing dirt to mix with the grease. -scott