I understand the cheaper ones don't have enough standard memory to accept useful-size maps unless you buy additional memory.
One you might consider is the Garmin iQUE 3600 which is a PDA and GPS combined. I've Googled and found it listed for under US$600 including 256 megabyte SD memory card.
This surely includes the USA map data, which won't be of much use to you. That would be a major problem when buying in the States for use in Europe.
The Garmin V is another possibility. Get plenty of memory. Again a question of getting a European database if buying in the USA. It's in their triagular cross-section, which I find very handy on a car's dashboard. Forget the mounting bracket - use Velcro. I had a Garmin II+ in the same shape, but it went when I sold the boat.
Realize that internal batteries get eaten pretty fast in the fancier models. You'll want an external power arrangement.
Two good noncommercial sites:
http://www.gpsinformation.net/
http://www.edu-observatory.org/gps/gps.html
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