Money is fungible, so I would be sympathetic to an argument that claimed he had made in the vicinity of $40k from selling drugs (which could not be confiscated for whatever reason, maybe he spent it all on drugs for his own use or something) and so it was justified to seize his car.

But from the way it's described, I don't see why the state doesn't think it can justify confiscating an arbitrarily large amount of property from a person who has committed an arbitrarily small drug crime. e.g. if this guy owned a $400,000 house and sold $20 worth of drugs out of it, can they take his house?