I'm replacing the old factory nav with a new garmin aftermarket one, but I'd like to keep the functionality of the gps audio (and phone calls that go through the garmin's bluetooth) going through the factory stereo speakers and muting/attenuating the radio/cd.

I think I have found one unit that will work:
http://www.newministuff.com/new/shop...uctshow&id=188

However that one is very costly due to the currency conversion, VAT, and shipping (comes to over $130 by my calculations). Are there any cheaper options?

I looked into doing it myself, and even though the nav input into the stereo seems to be an easily accessible analog signal, it looks like the mute is something complicated on the can/i-bus which means a kit would probably be best.