I Think the Colorado is a good unit, But I think you might have to purchase unlock codes to get the detailed chesapeake bay charts.
The mapsource CD ( accesories) allows you to plan routes and trips at home on your laptop or desktop and then you can upload to the handheld.
I'd check with garmin or this vendor...on the level of chart detail.
I have the Garmin 76 csx and had to purchase unlock codes.
if so, you've got to figure in another expense.