Garmin Legend fits all your criteria, i have one it works great! Waterproof i think or it floats at least. dustproof, and you can hold 8 megabites of maps on there. We have a program with THE US AND SOUTH AMERICA on our laptop and we download what we need from that or we can use both at the same time if you have a car/laptop charger.

All for about $200 <img src="images/graemlins/laugh.gif" alt="" />