score:3
There is the KorriGo card, which covers a fair amount of trains and buses in Brittany within a certain time period.
Some possible plans to use with the KorriGo card:
Upvote:2
Have you had a look into https://www.ter.sncf.com/bretagne/tarifs-cartes/pass-ter-breizhgo ?
My impression is that buses in Bretagne typically cost 2.50 Euros and are so infrequent that you are unlikely to take more than two per day.