lester,
I was looking at finishing my simrad Cx44e with radar which comes to the tune of about $3900.00. After looking into XM and what I could and couldnt do the XM won out. There are many units you can go with to get XM weather and or radio. I opted for the Garmin 545 coastal - $810
GXM31 Smart Antenna - $216
Garmin G2Vision chart VUS512L - $330
A one time XM activation charge $50
And a month to month suscription $30-$50 per month depending on the package you get.
XM WX Satellite Weather for Marine Service and Pricing
I went with the 545 mainly because of its good reviews and it is big enough to use as a backup Chart plotter on the boat that is why you see the G2 Vision chart. I am going to leave this unit set in TDs instead of Lat and Long because everyone where we fish uses TDs and it is a pain to switch one unit back and forth. I did see some of the 400 series units on ebay for about 1/2 the price of the package I opted for.