train from Prague to Regensburg

You could fly.

Hi, Kelly, I would book your trip from Prague to Regensburg on Deutsche Bahn, which is the German national railroad and is at this URL: https://int.bahn.de/en

First, plug in your date, then your departing station (Prague) and arrival station (Regensburg Hbf), and it will show you the trains that are available. Make sure you put the approximate time period you want to leave. It will give you a list of options. When I'm looking at it just now, the trip takes a hair over 4 hours. 2nd class is perfectly acceptable, and I've taken it many times, but you can always choose first class. If you're picky about your seats, then get a seat reservation.

With regards to Ljubljana from Budapest, you could fly, or you could take FlixBus, which is a pretty inexpensive way to travel. The bus ride from Budapest to Ljubljana only takes 6 hours as opposed to the 8 hrs. you're seeing via train. You would probably spend about the same amount of time getting to the airport, waiting for your flight and then the actual flight and so on. It's up to you which one you choose. What's worse, I've taken FlixBus before and have no problems with it. It's very clean and comfortable and very reliable. I wouldn't hesitate to take it again. https://shop.global.flixbus.com/

For Prague to Regensburg I'd personally use the website for Czech trains at https://www.cd.cz/en - you can get direct trains for 423czk to 623czk ($20-$31)

The German trains are a little over €30, so I don't think there's any real difference in price. Plus they take the same amount of time (4 hours). Regardless, you could go with either DB or CD without any problems.

That said, a lot will depend on the time of day and what day of the week you leave, so what I would do is check fares and tickets on both the German and Czech sites, and see which one saves you the most money. 😊

The operator of the route is České dráhy and the German private operator Die Länderbahn specifically their brand ALX, as the Bavorský expres (Bavarian Express). Purchasing the tickets on Bahn.com the current price is €36.50 and at today's exchange rate that would be $43. If purchased at cd.cz the tickets are as low as 423czk ($20) up to 623czk ($31) - a $12-$23 difference. Also purchasing through the Czech website you can pick and reserve your seats for free.

Flying isn't an option from Budapest, at least as a direct flight. Looking at the Ljubljana airport entry on Wikipedia (which is usually accurate) there are no flights between that city pair.

Just to be double certain the airport website itself shows no such flights- https://www.lju-airport.si/en/flights/timetable/

There is a direct train leaving Prague every two hours, at 35 minutes past the odd hour (7:35, EX360; 9:35, EX358; 11:35, EX356; 13:35, EX354, etc) It's the same train mentioned by several people above and takes 4H6min with no changes.