Thank you for all the helpful replies!
Our use is mostly to get ashore after anchoring, so far only in the U.S. Northeast (ME, NH, MA, RI). After spending a couple of hours shuttling crew while rowing 300-400 yards to shore back and forth, I'm considering would would be the best option to do it more efficiently.
So, one is a freshwater trolling motor like the Minn Kota from West Marine
which you say would work fine even in saltwater, provided it's rinsed afterwards (e.g. with a cockpit shower or slip hose). It's only $149 new + a 12V battery.
Any idea how long a battery for this motor would last in terms of range, and how much it would weigh? The trolling motor is 30 Lbs. The battery must be another 20 at least, I'm guessing? Could it be charged like the house system batteries by the inboard motor, by swapping it with one of them?
I'm also considering old Johnson and Evinrude 2-3 HP 2-strokes, as these seem to be the cheapest, lightest and available in the area. Didn't see any inexpensive Yamaha 2HP outboards on the local craigslist. The 4-strokes seem to be at least $500.
If I have to row (don't mind the physical labor, more the time it takes with multiple trips with >3 people aboard), I was thinking of fashioning a rudder for the Redcrest out of PVC pipe, some fittings, and a piece of oar or paddle so I don't go in circles. Has anyone here built something like that? It seems pretty simple and theoretically should work well
I am also thinking of trying out a kayak paddle which I use with our canoe very efficiently, but I'm guessing on a flat bottom rubber dinghy it wouldn't work so well - unless it has a rudder. Thoughts?