Depends on what kind of used car you're thinking of. (I'm being anal; it's a weird analogy given you can probably get a used car for <$100)

Anyway, the cost of ebikes has gone down a lot over the years, especially as more and more competition shows up and production of various parts (batteries, motors, control units) has scaled up. I just had a quick boggle, ebikes start at around €1200 at the moment (cheaper too, but those are folding bikes).