I have a late model GM radio similar to what TopNotch refers to. It has a cassette player instead of a CD. It has theft-lok if you want to activate it. I have turned it off. You will have to get the volume/on-off knob. It/s $6 at a GM dealer, or you can grab one at the local pull-a-part. $45
The wiring adaptor that allows you to install without cutting your factory harness includes the antenna adaptor, too. The kit is plug n play and costs $30.