What would be the cost of transportation to Amersfoort from Frankfurt or Amsterdam? Maybe I could rent a car and drive.

I can't tell you what it costs, but it would be an experience if you have
never driven on the Autobahn. Remember there's no generic speed limit
in Germany. This could be exciting, but it can also be nervewrecking.

It's not unusual that average speeds are 80 km/h on the right lane,
and 180 km/h on the left lane. Always check your mirrors twice or
three times before overtaking.

Driving in the weekend is more relaxed (and faster), when trucks are
banned on the Autobahn.

Pim