Help with the most current SRX GPS Disc

I have a 2004 SRX V8 AWD with all of the "goodies" ( the wife's car). Purchased in July of 2004 and she has 4700 miles on her!

Can someone provide me with the part number for the most current GPS disc for this 2004 SRX unit and the approximate purchase price.

I'm assuming that GM Parts Direct will be the best price source and if so, can someone tell me what they paid for the disc?

Is it not ridiculious that GM does not provide the new disc for around $100 as an "upgrade"; much like Microsoft does when the new version of Window or Microsoft Office/works becomes available? Or is that just me???

Any help with the part number and approximate price would be greatly appreciated.