Germany is not Hungary. Labour Costs in Germany are higher than in Hungary. So don't expect that the bus tickets are the same price. Hungary is not a good benchmark for Germany.
It is definitely possible to find train tickets for less than 100 EUR between Munich and Berlin. I can point you to what I have written elsewhere:
The strategy to find a "cheap" ticket, for IC or ICE trains, is the
same as if you are looking for "cheap" flight tickets. The earlier you
book the more chances you have to make a good deal. Moreover, avoid
peak times, like Friday evening or Sunday evening. In the past I have
made some good deals on Wednesdays ... Flexibility pays off. Also
check the DB's search engine for saver fares.
If you travel frequently, you might consider to buy a Bahncard. This
entitles you to discounted fares, as well as other advantages.
But it is possible to travel cheaper by train. From Monday to Friday you can travel on a so-called "Quer durchs Land Ticket". And on the weekends you can use a "Schönes Wochenende Ticket". These tickets costs 44 EUR and 42 EUR for one person. If you are more than one person, the price per person is highly digressive. In the most extreme case, if you are 5 and you travel on a weekend, you end up by paying 8.40 EUR per person!
With these tickets you can travel all over Germany in regional and local trains. You cannot use IC, EC, or ICE trains. From Berlin to Munich will take you 10 to 11 hours. That's almost the double of the travel time of an ICE train. But, it's pretty close to the duration of a bus trip.