I have used a 40lb thrust trolling motor that I have been using for purposes like traversing under bridges, getting on / off a (small) lake if the wind died, etc, so pretty similar to what the OP is trying to do. For saltwater you can get trolling motors that are more corrosion resistant.
I tend to bring the motor selectively, so I decided against a permanent installation. I had considered finding a trolling motor socket and running a fixed set of large gauge cables under the coaming forward. The cables need to be of a reasonable diameter so that the voltage drop over the distance is acceptable.
The shop I bought them from had a crimping tool that they could lend me for crimping the connectors.
With a single Deep Cycle battery I can run for about 35-40 mins at full power, until I sense that the motor is slowing a bit, which seems to happen around 50% discharge, which is the limit for the batter. I usually bring two batteries, that gives me another 35-40 mins. If I run the motor at setting 4 instead of 5, the run time nearly doubles, but the speed is only 35% less, so there's a net increase in distance, but it requires more patience
Usually, if I motor that long, the wind decides to come back, and because the DS easily sails faster than the trolling motor pushes it, I'm back sailing. Maintenance is minimal (topping off the batteries when not in use, mostly), and even with getting a new battery every 4 years on average, the total expense is pretty low. Something like $40 a year, averaged.