The arrival in the 1990s of the cheap discount tickets and cheaper airlines....really bulked up in-country flights. A flight from Hamburg to Munich is roughly $110 (in the non-tourist season), round-trip. From Berlin to Munich, it’s $85 round-trip.
But you can travel from Hamburg to Munich by car under 7 hours and under $50 in gas. You can take 4 more people with you. Or you may travel faster in a faster car.
One thing I do like about Europe is the train system. Very convenient and inexpensive.