O2 Sensor problems of the 2009 Dodge Charger

2009 Dodge Charger sxt, purchased back in may 2010, starting having check engine light problems in October 2010. The check engine light reads that I have a failure within my oxygen sensors. Purchased car used at 36, 252 miles. Woo hoo, the warranty on this car expired at 36,00 miles. I took the car into the "authorize" Chrysler dealership of whom charged me $99. 00 just to even look at my car, they called it a diagnostic fee from which they just hook car up to a portable computer and let the computer read the engine code. (the same thing that autozone or advanced auto parts does for free). They ran there machine on my car, read the code, and made me wait for about hour just so they could make me think they were actually doing something special when clearly I can see whats going on in the garage. Finally when they figured that I've waited long enough, the only thing they told me was that I had a bad oxygen sensor, shocker, since I already knew this because I took it to autozone were they ran the code, for free. Chyrlser said it would be around $300 to fix this problem. I was livid when they told me this and asked them to break down the $300 cost because I knew for fact that the parts were know more than $50. They told me parts were $63, and the rest was labor. Are you for real. It takes literally 2 minutes to change out an oxygen sensor, all you do is unplug the old one and insert the new one. I would do it myself if I had a car lift. I eventually ended up taking the car to an independent mechanic who perceded to fix my car for only $100. Surprise surprise, 2 days later my check engine light comes back on. I take it back to Dodge who again charges me another $99 only to tell me that the mechanice "changed the wrong on", really, ok, not. Took back to the other mechanic who changed out other O2 sensor for free. Check engine light came back on. Took back Chrysler dealership and they said he change the wrong one again, really, know really. Dodge/Chrysler/Jeep sucks.