For the speed (120mph) and the limited stops, you'll be paying a pretty penny to travel on an ICE from/to/within Germany. And, once onboard, the cost of WiFi (no, it's not free) just adds to the trip price. Our one-way ticket (with seat reservation) was 115 Euro. Tack on a few purchases of the 4.95 Euro plan to cover the 3.5-hour trip, and we could've just flown. But that's no fun if there's a highspeed train available!
The lesson to take away from all this? When budgeting your European spending, do factor in some float money to cover WiFi costs encountered on trains, at airports, in hotels and even possibly at cafes. It adds up quickly.