Train from Frankfurt to Budapest

The fastest connections I see on Deutsche Bahn last 10 hours and involve a change in Linz. Is this what you want? Personally, I would rather fly.

If you really want to ride the train this long, purchase your tickets from the Deutsche Bahn website if you want to save money. It's too early to buy tickets for a trip in October, but when they do go on sale, the earlier you buy, the cheaper the cost. However, this will lock you into riding a specific train at a specific time.

The Board Bistro on Deutsche Bahn ICE trains is open to everyone, not just first class. The only difference is that first class offers waiter service. But if I was on a train for 10 hours, I think I might want to walk over to the bistro myself. Overall, for most casual travelers, first class probably isn't worth the extra cost. It's designed more to provide extra work space for business travelers than for casual traveler comfort. Most posters here (myself included) find second class perfectly comfortable and adequate. The difference is much smaller than between classes on airplanes.

I also would suggest flying that route. I use a rule of thumb of about 6 hours - 6 hours by train and I usually take the train. Much more than that and I tend to fly.

I agree that I would fly a segment that took this long by train. To find flights, use Skyscanner: http://www.skyscanner.com/

Walter has updated his route on this post: https://community.ricksteves.com/travel-forum/germany/correction-train-from-munich-to-budapest