Among social media, Mastodon (and anything Fediverse) has it the worst, obviously, but Telegram and Whatsapp are rife with spams and scams, Twitter back when it still had third-party apps was rife with credential and token compromises (mostly used to shill cryptocurrencies).
As for the price tag reference - we've seen that with SMS. It used to be the case that sending SMS cost real money, something like 20 ct/message. It was prohibitively expensive to run SMS campaigns. But nowadays? It's effectively free at scale if you go the legit route and practically free if you manage to get someone's account at one of the tons of bulk SMS providers compromised. Apple's iMessage similarly makes bad actors pay a lot, because access to it is tied to a legitimate or stolen Apple product serial.
