top end rebuild

Hi all,
first of all, thanks for all your help so far. I am thinking about picking up a cheap 98 kx 125 that seems to be in great shape with lots of extras like exhaust, handle bars, bark busters, etc, but the engine is siezed. the person says that the piston ring is seized. I was wondering first of all, what kind of price range I can expect to spend on getting it fixed? I know its hard to say without getting in there and taking a look at it but a general idea would be great. also, does anyone have some good links on how to tear it apart and get everything replaced? I have a friend that is gonna help me do it but I would like to read up on it before we tear into it. I am very novice when it comes to engines so explanations and pictures would be awesome. thanks again,
Jim

thanks for the replies, what should I look for when tearing it down and what should I plan of replacing for sure? also, I have a 97 kx125 that I am planing on doing a top end on as preventative maintance, runs good, but what all needs to be replaced when doing a normal top end? piston, rings, top end gasket, any thing else? anyone know where to download a service manual for either of these bikes?
thanks