$40etrex (ebay) with $20 RAM handlebar mount (gpscity) is still a solid option, not that i'd say the maps are a huge help, but at least you get the land masses on the map and a bread crumb trail to follow home and it keeps track of miles as well. I can definitely say that my etrex has bailed me out several times and is more than adequate if you are familiar with your local waters, I wouldn't want to trust it to save my azz in a new area.
I also have a huge 4 1/2 garmin but honestly its too large even for a big ski, but the details are pretty amazing, It really only seriously helped me once on a poker run, the rest of the time the extrex was more than enough.
I tried the phone mount once for an older sony experia waterproof phone and it worked ok but it didn't do well in bright sunlight, very hard for me to see the map.