Relay for Reddit app stays as one of the few remaining third party apps for Reddit and they are forced to go to a subscription model but the cost of such a subscription is related to how many API calls per user are done.
This screenshot was taken from the yet working patched Sync for Reddit app.
And mind you, the only reason early SMS messages were so expensive was… because they could. The SMS protocol literally piggybacks on existing handshake datastreams already present in the GSM standard and only requires adding a small message handling server to a carrier’s network. But because it was new and a novelty, and little to no competition existed in the cellular space, cellular companies (being the money grabbing corporations they are) would charge exorbitant rates for this add-on service that cost almost nothing to provide. Which is effectively reddit’s stance too… fuck you, pay me.
SMS was free on some networks initially. They only even realised they could charge for it later.