You can spend from about 100 bucks up to a couple thousand, if you so desire,
A good starter one would be the Garmin eTrex, or the Etrex camo, which has fishing/ game tables with it. They are supposed to tell when the best time to hunt/ fish are.
The big name brands in GPS are Garmin, Magellan, and Lowrance.
Several of the garmin models come with or are compatable with mapsource software, and there are even several different CDs with "blue water maps" that you can use to find your way around the gulf, and the east and west coasts.
Each area costs a little more $$ to "unlock" on the cd, but you can buy just your area for a pretty reasonable price.
Here is about the best place I found on the web to get GPS stuff:
www.gpscity.com
and here:
www.gpsnow.com
one moe time:
www.advancedgps.com
Those ought to keep you drooling over all the neat gadgetry for a while.