I've been looking at cheaper used EVs for a second car. There are lots of used LEAFs out there, some Smart EDs, and a couple of Focus Electrics, which look really nice if you don't mind the short range, but aren't very popular at all. These cars seem to drop in value a lot for the used market. I saw several that were not all that old going for under $10,000.
Teslas seem to retain their value better. I'd guess it's partly because the car is more desirable, and partly because Tesla treats their batteries a lot better, so they can be expected to last longer. The LEAF in particular was known for a while for losing quite a bit of range in just a few years.
As far as how they'll retain their value in the long term, it's hard to say. EVs should lose less value due to things like drivetrain wear, since you don't have a bazillion moving parts in an engine and transmission to go wrong. But they'll lose more value to battery degradation. Much will hinge on how well the batteries age and how much they cost to replace in 10+ years.