Pontiac Repair: aftermarket radio install; 03 Montana, radio speakers, computer module

Question
I got a relly great deal on an aftermarket radio.  However, my excitement faded as the tech at the store told me that it requires a harness that costs about $121.  I thought I was being taken, so I called my local car audio install experts, and was told the exact same price... something to do with a computer module that is integrated with the factory stereo/CD?  Is this accurate?  I have seen various sites selling harnesses, listed for this year/model, that are basic harnesses.  I do not want to risk ruining the computer and/or electronics, as that is what, I was told by both install techs, would happen, if I did not get it installed with the proper harness/electronics.  What are my options?  My Montana is all power, but does not have Onstar, if that makes a difference.  Thanks,  Bud

Answer
Hey Bud:

Yes it does make a difference. The radio is tied into other modules on that car. The Chime for the door/headlight/seatbelt uses the radio speakers. If the car did have onstar it uses the radio speakers. I don't think you will screw up any thing by using the correct harness/adaptor for the radio to work on that exact year/model van but you never know. I would look into getting the correct radio to replace the one that's in the van right now if it's broken or where you just looking to upgrade what you have? If you get an exact replacement "gm exchange" they are usually $250.00 from the dealer. You can also look on Ebay Just get the EXACT same part # radio. the cost of the radio you bough + the harness is more than likely just about the price of an excahnge unit. Weigh you options... Good luck :}