2003 Dodge Caravan Engine Light/Oxygen Sensor

I have a 2003 Dodge Caravan SE 3.3L. Today the engine light came on. I had to get an emissions test today (of course!) And the vehicle failed. I was told the particular part wrong was the "O2 Sensor Heater Circuit Bank 1 Sensor 1". The engine code I got was "P0135". I did a little calling around, first to the local Dodge Dealership, who quoted me $325 + tax for parts and labor to fix the issue. I called my local Schucks Auto Supply and they sell two different types of sensors. The first is a "universal" model that costs $64. The second is the exact type for my vehicle spefically, and that runs $125. What I would like to know is, how easy is this to replace myself? Is it something that would be fairly simple? And also, is the dealership ripping me off for that price? Thank you!