I think they would happily negotiate that price down to nil per month, if they could be absolutely sure a 'device' on your account wasn't actually your cousin 'sharing' your cellular account to save a bit of money.

Anecdotally, I've seen it closer to $10/month for car or smartwatch, and $0 for Kindle though I'm not entirely sure if they're still shipping cellular. Tablets are closer to that $20-$30, though.