TMT,
I've never tried the bus, but Metrolink is very cycling friendly.
I caught the 8XX train from Orange station and exited at Oceanside. From there, start many rides inland or simply come back up PCH. Last time I scouted an inland route it was to Double Peak and back, but this seemed a little too challenging at my current fitness level.
Chances are you will meet like minded folks on the train riding in the bike car and security will not be a problem.
You can ride anywhere in a day for $10 (last time I checked).