It seems to use the conversion bonus where you discard an old fossil car to a new more efficient one, it can't use the EV bonus because it needs to be a new car, in this case this is a 5000€ bonus, if the law was changed to accept conversion it would make the whole thing free.

https://www.service-public.fr/particuliers/vosdroits/F34014

That still seems way too cheap to me. A good battery pack would cost that much.

And as someone else said, it's still an old(er) vehicle - any incident may lead to the vehicle being totaled from an insurance point of view.

This may be OK for some consumers, but it could a big financial surprise to most.