Avionics Cost Question

For you avionics guys out there...what should it cost to have an avionics
shop install an audio input jack in my panel as an add-on to my
panel-mounted stereo intercom?

We have a Narco CP-136 audio panel, and a PS Engineering CD/Intercom. I'm
assuming the input jack has to "patch in" to the intercom somewhere.
(Frustratingly, a jack already exists for the back-seat passengers only.
It's a nice feature so that they can listen to their own music in back --
but we don't have the same option in the front seats.)

I would like to use this input jack to connect a portable XM radio receiver
or an Ipod-type device.

Thanks in advance!
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"