Hugh, I tend to trust www.Edmunds.com
I made a few assumptions and came up with what is attached below.
Why are you selling? I think if you put a price on there of $22,000.oo and are willing to bend a bit, you should be able to get rid of it. Especially with winter around the corner. Just remember that GM is clearing the lots of 2004s and they have 0.0% financing for qualified buyers which may take some of your business.