I have an etrex legend as a back up, which I find is perfectly adequate.
It came with basic base map and the cd has nautical lights/bouys and wrecks to add.
It can also take blue charts if you wanted to but as the screen is only B&W personally I have never bothered.
I use garmins cycle handle bar mount to clip it to the grab rail if I need it.
I do use with the Garmins Road and Recreation map data when I am cycling or hiking.
currently £106!! on expansys