There are saltwater trolling motors that have up to 60 pounds of thrust that would operate off a single 12-volt deep cycle battery. Much cheaper than even a small gas outboard, although the weight might be a wash as the motor is not heavy but the battery is.
West Marine sent me a small catalog back in March that featured two electric outboards of which I was previously unaware. Both are manufactured by Torqeedo, Starnberg, Germany. One is the Travel 801 Electric Outboard that produces nearly 73 pounds of thrust and has a battery as an integral part of the motor. The entire unit weighs just under 27 pounds and is advertised as providing two hours of use per charge. Comes with a 110V AC charger. Also comes in short (29.3 inches) or long (33.9 inches) shaft. Price is listed as $1,599.
The other model is the Cruise 2.0 Electric outboard. Claims that it delivers the equivalent thrust of a 6 HP combustion engine. This is a 24V motor and appears to require the use of two 12V batteries linked in series. Also comes in short (24.6 inches) and long (29.3 inches) shaft version. The weight is 35 pounds for the short shaft and 36.4 pounds for the long shaft, still pretty light by outboard standards. It's a bit pricey at $2,299 and you'd need the two batteries. However,
fuel savings over the long haul would reduce the purchase price.
I haven't run a Google search on the web to see if any marine distributors would carry either of these motors at a lower cost than WM.
I have no link to the manufacturer or WM. I have used electric trolling motors and deep-cycle batteries for years on a 14-foot fishing boat on two local reservoirs that do not allow gas outboards. I actually used a trolling motor on a Catalina 22 for a while and I've seen J-24s use the higher-thrust 12V models, so using even a smaller one on a
dinghy would move it along smartly.