Buy train tickets in advance

Sorry you were shocked -- but if you were reading posts about advance purchase and also checking prices online, you should have been warned that the cheap tickets sell out and day-of fares are the highest (full fare) Just like buying walk-up airline tickets.

Glad you could buy a cheaper ticket to Vienna (which is, of course, a much shorter trip from Budapest than Munich is.) Did you get seat reservations as well ? We took that train last May on a Sunday and there were people without reservations standing in the aisles.

I'm also sorry to hear this but see that you asked your own question on the topic on 10/1 and received accurate answers, though less detailed than on many similar threads. When you did your online research, the DB screen would have displayed both the Savings Fare (€ 39) and Flexpreis (full fare of € 127) next to each other (both prices in 2nd class). Clicking on the offers leads to the fare rules, including "A limited number of tickets are available for purchase up to one day before date of travel."

Another possible lesson is to fly to a place that you want to visit, or said another way, spend at least a night in your flight arrival city. Then, you don't have to balance advance-purchase savings against such a strong possibility of flight delays.

Alternatively, if you need several days of train travel, especially in a region like this where seat reservations are not required, then a rail pass can provide a balance of price and flexibility.

How can people not understand this concept - buy ahead at cheaper prices. The longer you wait the more expensive it gets.

If you read a previous post by the OP, they did not prepurchase tickets because the trip was on the day of arrival, after their flight. Many people don't prebook tickets in case of delay. I'm guessing the OP did not realize there could be such a large difference in price between the two types of tickets.

I was told from this site that this is also true for the budget airlines. Buy early for best fares.

Question: what is the actual difference in first vs. second class on European railways.

Also OP, you haven't purchased tickets on Amtrack here in the USA either. Same in the USA, but maybe not that large of difference.

Question: what is the actual difference in first vs. second class on European railways.

Answer: 50%
Second class is 2+2 seating, first class is 2+1, with proportional increase in seat spacing. That makes about 50% increase in the acreage per passenger. Sometimes you get food thrown in in first class, but usually only on high speed trains.
Second class is more space than first class on aircraft, and you can get up and walk around easier than on a plane.

If you are a couple, the one facing one seats across a table in first class gives you a personal space.
A fair price for more space, it is up to you whether you wish to pay for extra space.

While the seats are wider, I don't really find much increase in leg space. Something maybe a little off. Assume the 39E for for a single compared to 130 E. But if the 39 was a deep discount advance save then 130 might not be unreasonable. The low to high on a lot of the long runs in Italy will be double and often 50% more added. So a 40E ticket could hit a 100E for the walk up price.