I put a Swytch front wheel conversion on one of my road bikes. It works great for my tired old body. haha
One can wait months for its arrival, but I think it's totally worth it. I use it a few times monthly.
Approx $700, while adding about ten pounds to my 18-pounder. (I carry a spare battery.)
You can't come close to that result without spending big bucks.
I achieve an average of 25 miles on each battery, but exert considerable pedaling effort.
And if I exhaust my batteries, I can still pedal home. Try that on a fifty-pound behemoth!