the o2 sensors are 4 different part numbers for each sensor on the car. and yes they are specific. the ecu is programmed to read only oem, therefore if you buy aftermarket, it wont last you one day. yes you have to get them from the dealer and no you dont have to pay for installation. guy a o2 sensor socket, and dot it yourself. that will save you the money, or you could grab a 7/8 wrench that wont open up on you easily, and do it that way.
before you post something like this again, i suggest you search a bit. there are tons of threads about this and they all say the same thing. search. surprised that you didnt get torn a new one yet...
YOU DONT DRIVE A PIECE OF JUNK SO DONT FIX IT LIKE ONE.
IF YOUR NOT GONNA DO THE JOB RIGHT THE FIRST TIME, YOU SHOULDNT BE DOING IT AT ALL