I was wondering how much a CV joint cost to be repaired by yourself.
Also how difficult is it. and How long will it last before it totally goes?

Are you talking rebuilding the joint(s) or just rebooting? If the car has a lot of miles on the axles your better off replacing the whole axle, usually around $65.00 + core but you ge that back. Rebooting(2 joints) will cost just about as much, take longer, & very messy. I have no idea how much it would cost to rebuild because I, it's always a replacement axle with bad joints.