Train Tickets

You are just too early. This is train travel. When I travelled Budapest to Prague I just bought the ticket at the station in Budapest.
You can safely wait till October.

Wait till the first of August and try MAV. If it still doesnt work, come back.

I was able to set up a purchase of Roundtrip Prague to Budapest train tix on the Czech National Railway site www.cd.cz. for late October. The tickets in 2nd class are about 600 Czech Crowns ( US$25) which includes the reservation. There is a further discount for Seniors. I only needed to add my credit card number to complete the purchase.

I use the app that Kenko mentions and it is great ,I am in Czech republic several times a year and use this app for all my train travel. I have used it for Bratislava to Brno and know I can use it for trips from any Czech city to other cities in nearby countries.

MAV App for buying the tickets? Go to the website and see how your luck holds out. I buy tickets on line quite often, then they transfer to my phone App. https://jegy.mav.hu/jegy/vonat

For your trip I checked the MAV site again today.

For all of October the rates are current and working. About $25 Prague to Budapest.

But you indicated you would be returning in November and the MAV site hasn't posted updated November ticket prices yet. Yes, you can still buy a ticket and there are prices shown, but they are goofy high. In a week or two they will be the same as the current prices for October, about $25.

i suspect you will end up buyng from the Czechs, thats fine. Which ever, do download their APP. I presume the Czechs have one. Makes displaying your tickets on the train much easier.

Having said all of this about trains from Prague to Budapest, if the timing works, it a lot faster to fly. And if you travel light doesnt have to cost much more. I did all the math once including travel time to and from airports and train stations, early arrivals etc and you save about 3 hours on the plane. And if you consider that maybe the first hour in the airport isnt "early arrival" its breakfast, then it saves 4 hours.

Also check RegioJet. The will use Kelenföld Station in Budapest, but thats not the end of th world. Its on the M4 metro line. I looked and they have prices up for October and Noveber. Doesnt look cheaper than the national companies, but check out what comes with the ticket. I understand it can be a bit nicer than the national companes. Dont know though. https://regiojet.com/

With European train and transit companies I've had better success with their iPhone apps rather than with their websites. Sometimes a different browser on my PC solves the issue.

On the MAV site, as of today, 11 am, 6 August in Budapest the cheap rates are showing through 4 November then they get googy high. I suspect tomorrow the cheap rates will show through 5 November, etc.