Where to go to have a signature witnessed (Munich)

I´m an Australian on a prolonged stay in Munich and I have a statutory declaration to sign to be witnessed by an appropriately qualified person. I´ve been told that notaries etc. charge a huge fee for their time and things are done differently in Germany than in Australia with these matters. Does anyone have any ideas? And can anyone tell me how to explain my situation in German? My German is pretty good for everyday use, but not for legal jargon. Thanks.