I am arriving in Frankfurt from the USA and leaving immediately for Munich. We can either rent a car or take the train from the airport. If we rent a car, we will probably stop in Rothenburg overnight because I am reluctant to drive the entire distance to Munich while recovering from jet lag. Since we prefer to arrive in Munich on the same day, I am investigating taking the train to Munich and renting a car in Munich a few days later for the balance of our trip.

I visited the Deutsche Bahn website and saw that an advance ticket to Munich cost about 59 EUR. I am reluctant to purchase a ticket in advance just in case our flight is delayed, which has happened to me before.

If I wait until we arrive, will it cost much more to purchase a train ticket at the last minute at the airport?

When you look up fares on dbahn.de, you'll see Savings Fare (if available) and Standard Fare. Standard Fare is the price you will pay if you buy your ticket on the day of travel. For that route, it looks like standard fare is 95 euro.

Yhete is some kind of plan, where you can take advantage of the reduced Internet advanced fares without comitting to a specific train. Take another look at ww.de.bahn. for the details.

Have you checked your flight schedule to see if you can change to MUC? Or, maybe add that at part of your flight, as it should be little or no extra charge?

On bahn.de, the sooner you book, the better it is. Last minute (up to 2 days before departure) ICE bahn tickets are available from www.ltur.de starting at 25€. You'll end up booking on the original bahn site, while those fares aren't available directly at bahn.de

Have a word with your airline, and check if they have Rail&Fly tickets. These are flexible so you can take any train upon arrival.