Don't know what the story is now but only 10 years ago there was only one bus a week (on Tuesdays) which left Dundalk at 09:00, reached Cavan about 11:00. Left again for Dundalk at 13:30. How useless was that? The only people you ever seen on it were pensioners.
I do know that there are a number of private bus companies going from the likes of Baileborough and Kingscourt to the RTC in Dundalk but I don't know about Cavan town. To be honest you are probably better off moving to Dundalk, that journey every day would kill you.