This calculator might help:
https://www.efficiencymaine.com/at-h...st-comparison/
I entered values for 5 gallons a day, price of oil $5.80 a gallon, and cost of electricity $.1658 per kwH. The result was $74 a year for a tankless coil and $55 a year for the electric water heater.
That doesn't seem right. I think both figures are too low, otherwise I would not have turned off the hot water tank. The calculator doesn't include the size of the water tank. In any case, "oil boiler with tankless coil" is the most expensive on the bar chart.