[Bcube]

First you need to accept that you will probably have to pay "something". I don't think you will get away without opening your wallet.

Second, you need to do some research - get some basic understanding of what was done to fix the problem. The CPO warranty clearly states that the radio and any components of that radio system is not covered. OTOH, electrical issues are covered. So you need to find out what junction box was replaced or fixed to see if it can be determined if this was an electrical issue due to the headlights, relays, etc or whether this junction box is purely a radio component.

Third, Talk to the Service Manager directly. Don't waste any more time with the Service Rep - you already know his position. Time to move up the chain of command. Discuss the issue with SM, see what can be done to reduce the price. Maybe some of the labor time can be reduced. Parts at dealer cost, etc. Keep cool, be polite, don't lose your temper. Explain that you were told by the Service Rep that this was covered under warranty and thus wasn't given an estimate otherwise you would have reconsidered having the work done. (that is, if that is the truth, I am guessing)

If the SM doesn't satisfy, then move up to the General Manager or Owner or have the GM as part of the discussion with the SM. But the biggest thing is don't go in with both guns blazing; trying to negotiate in anger with folks you have put on the defensive will be futile.