What GPS to buy?
I just purchased a Magellan 315, it works great. I chose not to go with a map version because I found the display to small to be practical, for me anyway. With the 315 you can interface it with a laptop and charting software, which is more expensive baut very easy to read and manipulate. The 315 on its own has all the features you really need to sail with lots of routes and waypoint storage and a huge display.
Good luck in Your search. I did look at Garmin and found thhe price to be a little bit high.