Intake Manifold gaskets are a breeze to replace. Before you start I would get the Haynes manual for your car. you can get it at any auto parts store, read it and then go ahead and start.
Just remember to keep track of your parts and clean them before you install them back on your engine. Buy some wire ties so you can keep hoses and wires out of your way.
When removing the old gasket be sure not to damage the face on the intake or engine.
The dealer charging you $600.00 to do it is average price but why pay that when you can do it in a few hours. and pay yourself.