What would cause a 96 civic to...

Overheat and start shaking???

Guy at work told me he was driving home and all of a sudden his car was over heating and shaking. its a civic ex with 120K and auto. He took it to a mechanic and they told him his head gasket is blown.

Any idea what it could be, they wanna charge him 1,200 to fix it...Are they ripping him off. i would guess it would be easy to replace a head gasket