It's easy to get to Berchtesgaden from Salzburg.
)1 There is an hourly bus, the Watzmann Express, RVO 840,, that leaves Salzburg Hbf and makes several stops in town, including Mirabell, before going to Berchtesgaden. The trip takes less than an hour.
2) You can also go by train via Freilassing. That takes a little over an hour.
The trains run all day until late evening; the last bus back to Salzburg is around 6 PM.
An RVO Tagesticket costs cost 10,- euro for an adult and covers not only the round trip bus to/from Berchtesgaden, but also most buses in Berchtesgaden including the bus to Kònigssee and the bus to Salzberg, where the special buses go up the private road (closed to cars) to the Eagles Nest.
A Bayern-Ticket, 26 euro for the first person, 6 euro for travelers 2 - 5, will cover the train round trip plus the same buses in Berchtesgaden as covered by the RVO TagesTicket.
Finally, if you want to take the bus, which is faster to Berchtesgaden, then stay later past the last bus time and come home on the train, you can use a BGL-TagesTicket Bus and Train.for 12,- euro per person. It covers the Waltmann Express to or from Salzburg, or the train via Freilassing, or one each way as well as the same buses in Berchtesgaden as the other two tickets.
I would take one day off of Salzburg and go by bus through the Salzkammergut to Hallstatt, spend the night in Hallstatt, then go by train from Hallstatt to Vienna.
