The PCV valve is on the backside of the engine block, it is made of metal
and actually has threads on it. Getting it out of there can be a trick,
you will have to do it from underneath the car. A Nissan Dealership should
charge about $55-$75 to replace it.

The PCV Valve is on the back of the engine block, under the intake
somewhere. It's not impossible to get to, but you'll have to get
underneath your car to get to it. Also the value is made of metal (cast
aluminum I believe) and has to be screwed in/out. I can't recall the size
(I want to say 15 or 17mm). It has about a 25cm rubber hose coming from
it's spout going into the intake from beneath. If this sounds like too
much fun to replace, you could pay a shop or dealer about $60-$75 to
replace it.