Just in case anyone searches for info on this - I know it's too late for Joannie - I visited the Eagle's Nest (Kehlsteinhaus) fom Salzburg last week. A bus from the Rathaus bus stop by the river took us to Berchtesgaden for Euros 8.50 (return, each), then another bus took us to what they call the "Dokumentation" stop for the mountain itself for 3 Euros (single). Admission to the Kehsteinhaus itself, including the special bus and lift was 15 Euros. So total cost was 20.50 less than the price of the escorted trip, which leaves from Mirabellplatz at 9 am and which can be pre-booked for 50 Euros.