Building your own battery saves thousands if not tens of thousands of dollars. Using a junkyard battery is even more affordable - but more work. Total cost for 50kWh should be around USD20,000.?

Using an inboard electric motor is also less expensive. If course it then needs shaft, seal, etc. making installation a bit more complicated. www.thunderstruck-EV.com has a pair of 35kW motors in line for 70kW total under USD10,000 ().?

It’s easier to buy a plug and play system, but you save significantly by assembling the system yourself. My guess is you could be up and running for around USD35,000-40,000 max. Plus the boat, of course. Still a lot of money.?