http://tinypic.com/view.php?pic=2janfrd&s=7
Compuserve $11 per hour, had "more than 250,000 subscribers".
The Source $8 per hour.
Delphi $6 per hour had a loyal but small (less than 10,000 users) following.
BIX $9 per hour.
There was also an ecosystem of apps to script connections to minimize time you spent online. You'd pick the forums you wanted to scrape new messages from, fetch them in one session, compose replies offline, and post the replies in a second session.
ADDED:Private systems didn't (ever?) have a time charge. The bigger ones usually still offered some lines for free users but offered preferred access for subscribers.
One of the things that kept me at the time on Delphi was 1) X-Files had a huge fanbase there and Chris Carter would regularly join the forums and 2) You could break out of the menus and get down to the VMS shell which is how I first learned something other than DOS/Windows.
I still racked up massive phone bills even with the offline readers.
I grew up in Ashtabula, Ohio, and the closest access numbers made the toll charges the greatest cost.
ADDED: BTW, in the early eighties, long distance rates were starting to come down but they were still in the tens of cents per minute so something over a dollar/minute in today's currency.
It was the first and only time I ever saw my dad visibly tremble with rage and turn red. ($400 80's bucks is a lot of 2019 bucks to spend on a video game.)