Like many things, the GPS you really want always costs $400.00.

Here are some of more popular models are shown below

The market leaders are Garmin, Magellin, Tom Tom, and Lowrance

The newest features that I think are critical in no particular order are:

Text  to speech - tells you to turn on Elm Street not just turn right in 100 yards

Searchable by name Points of Interest (POI).  Why go through menus if you don’t have to?

Route Avoidance - If you know a road is bad why take it?

Real Time Traffic Updates - usually only available in large cities and sometimes needs a separate attachment and a monthly subscription.

Bluetooth to your cell phone.  Some only can call from the POI database. Others can access your address book on your cell phone

The ones without these advanced features typically cost around $400.00 and look very much like the above.