Rather than use a tour from Salzburg, I would use one of many transport options to get to Berchtesgaden and use this tour company (note, I have no connection with this company).
My choice of tickets is the BGL Tagesticket Bus & Bahn, which allows you transport on either the train between Salzburg Hauptbahnhof and the Berchesgaden Hbf via Freilassing, Germany, or the Watzmann Express Bus (RVO 840), which goes directly through Austria to Berchtesgaden Hbf, and unlimited use of most of the buses of the RVO in Berchtesgaden for an entire day. It costs 12€/person.
Leave on the RVO bus from the Salzburg Hbf or one of several stops in Salzburg. It takes about 40 minutes. Then go to the nearby meeting place for the Eagles Nest Tours. Or just get on the 838 bus and go to the startup for the special buses to the Nest at Obersalzberg. For 33,50€ you get a roundtrip ticket up to the bus parking lot and use of the elevator from the bus parking lot to the Nest (admission to the Nest, actually, is free, but the road up is restricted to the buses - no private cars. If you hike all the way up, it doesn't cost you anything. Some people do it.)
If you study up, you should be able to do the tour on your own without a guide. Touring on your own is nice because you can spend as much or little time in the Nest as you want.
When you come back down to Obersalzberg, you might want to tour the Dokumentation Center, which has interesting exhibits on how the Nazis took over. You can also tour the bunkers that were in Obersalzberg and connected all the homes of the top Nazis.
Take the buses back to Berchtesgaden, see the town, and have dinner if you want. With the Tagesticket Bus & Bahn, you
can stay in Berchtesgaden well into the evening and take the train back. The last bus to Salzburg leaves around 6 PM. If you can make the bus you can instead use a regular RVO Tagesticket for 10,50€/adult. It includes everything of the BGL Tagesticket Bus & Bahn except the trains.