Budapest to Prague

I've known Laszlo for a lot of years. Good guy. http://www.silverwings.hu/

Or Daytrip.com or the train or even fly. (I would fly)

CK Shuttle also offers a private scenic transfer between the two cities - you would be able to specify stops along the way. Do you intend to do it all in a single day?

DRIVE: 6:00 hours at a minimum door to door with only a stop for gas or water. I have used all three.
CK Shuttle $784.00 plus the cost of any stops for sightseeing: https://www.ckshuttle.cz/
DayTrip.com $506 to $534.00 plus the cost of any stops for sightseeing: https://daytrip.com/ This doesn’t necessarily mean that DayTrip is less expensive than CK Shuttle. You will have to price out any stops along the way to compare.
Silver Wings, you will have to call or write for a quote: http://www.silverwings.hu/

FLIGHT: 4.30 hours minimum hotel door to hotel door with a 1:10 hour flight
RyanAir: $30 and up …. way up depending on how you pack and what day of the week and how far in advance you buy the ticket.

TRAIN: 7:46 hours minimum door to door with a 6:45 train ride.
MAV Tickets start at about $30.

If you are trying to do this in one day, I would stop in Brno for a few hours. I would take the train to Brno then a train to Budapest. I suspect you can do that for less than $150 for the 3 off you.

If you want to spend a night, then maybe CK Shuttle or DayTrip.com from Prague to Cesky Krumlov, spend the night and the next day either CK or DayTrip to the station in Vienna and the train to Budapest.