Finn here. For us, receiving SMS has never cost anything. Downloading MMS, that used to cost, but no-one uses those.
Sending an SMS could be as expensive as 20c when I was a kid. And an SMS is 160 characters. So if you wrote a long one it'd send it as three.
Then when I was about 12-13 there started being unlimited texting packages, which advertised as unlimited but after giving kids access to the service for a few months, limits were soon imposed to like a 1000 sms a month.