I have a 172c and love it. *You can get one on eBay for $320 shipped but you still need the BlueChart card for it which will set you back another $100+ so I guess that's out of your range for now. *
The black and white 172 is about $60 cheaper but I recommend going with a color unit because its easier to distinguish between marsh, water, and hard land. *
So $375 (including shipping) *is the best I found for you in Garmin fixed mount.
http://cgi.ebay.com/ebaymotors/GARMI...spagenameZWDVW
One thing I like about the 172, its fairly compact so it doesn't take up much dash space while the display is plenty big. *Some of the newer ones lik the 198 and so on are larger while not really having a bigger display? *I don't really understand why someone would pay more for a larger unit that doesn't really have a LARGER display? * ::)