Chrysler Repair: Check Engine Light, chrysler cirrus, free diagnostic test

Question
Hi Pete,
Before you replied I had the car towed to a dealer who just got back with me. He got a code of PO305 (among others that he didn't mention) and told me the car needs a good tune up. He did say that it was showing a #3 & #6 cylinder misfire. Here's what he wants to charge:
New plugs, ignition cable, and plenum gasket $273.17 total ($242 in labor)
Air Filter $32
Cleaning the injectors $112
Throttle body $100
Replacing 2 belts (serpentine and another) $134

For a grand total of $959.07 (526.70 labor, 432.37 parts)
WAY more than I can afford or want to spend.
I know that there are a few of these items that I can replace myself (air filter, spark plugs), but am not sure about the others. Any suggestions? Should I possibly take it to another shop as, in my opinion, dealers are more expensive than others? Could you let me know? I find it hard to believe that I couldn't do some of this work.
I also mistyped and the car is a 1999 (probably doesn't matter anyhow).
Thanks,
Jason

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Followup To
Question -
Hello. I have a 96 Chrysler Cirrus with 53,000 miles. This morning the check engine light went on and gave me a rough ride. When accelerating, I noticed a lot of hesitation. When driving home this afternoon, the light began to blink (probably signalling a more serious problem). I want to get the car into a shop, but feel I have been screwed too many times. I know I need the diagnostic done, but do you have any guesses what could be the problem? Thanks.
Answer -
hello jason
this could be bad 02 senser or idile contoll senser if you have a auto zone in your area they will do a free diagnostic test and juat write me back the code and i can tell you what senser it is and how to replace it pete

Answer
hello jason
yes bring it to another shop first if you can do the tune up your self and then if they find the same codes might read out ok you never know . i would not bring it to a dealler they are very high and you get the same work you get in a good shop such as mine and that would be half the price in my shop pete