The kind of car you have will determine the price (Honda a lot more $ than a Chevy, etc.)
Have you noticed any change in the idle speed when you start it up? Does it run a little rough at times, or have a loss of power?
About $70 and $5 for the gasket if you need a new one. I think it's on the intake manifold, on the back side. Easy to do, take it to an autoparts store and they will most likely walk you through it, a good one will even test it to see if you really need to replace it or maybe the connection is just dirty.