Advice on overnight train from Kraków to Budapest

Try this source: https://www.seat61.com/international-trains/trains-from-Krakow.htm#Krakow_to_Budapest

I did this many years ago. Bought my ticket in advance and it was very efficient. Would definitely do it again.

⁷Its 11.5 hours and not every night of the week. You will arrive about 08:30 in need of a shower that you wont get until checkin time at 14:00.

If you are a couple, a double will cost you about $300 for the two of you. A day train will cost about $80 for the two of you and take 9.5 hours but you lose the entire day. You can figure the other $220 is hotel cost; except a 4 star hotel in Budapest is less.

Ryanair nonstop will cost $45 (starting) and have you in Budapest for lunch.

All 3 are viable options.