Oxygen sensor

What should it cost to replace an o2 sensor. The dealer is trying to charge me $300. I sit difficult to do?

sometimes it is sometimes it isnt. it alsl depends on where it is. one I had to replce wouldnt come out for anything so I had to replace the exhaust manifold itself, just to replce the 02 sensor just to get it to pass emissions. but otherwise it just screwed out and screwed in and connect the wire. very easy....if it wants to come out.