Have you considered buying a Bafang E-bike kit and converting your current bike? Assuming you've got the skills to tear a bike down and rebuild it, it strikes me as the cost effective way to go. As well as not having to get used to a new bicycle.
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Syke
“No one in this world, so far as I know — and I have searched the records for years, and employed agents to help me — has ever lost money by underestimating the intelligence of the great masses of the plain people. Nor has anyone ever lost public office thereby.”
H.L. Mencken, (1926)