Cost also seems about the same. Go any further than paris or brussels and flying is almost certainly the quicker option and probablly cheaper
much, much cheaper. and especially much much MUCH faster. And easier to organize
Charleroi - Budapest with airplane: 2 hours, one airplane ticket
Brussels - Budapest with train: 15 hours or 20 hours, depending on the route you take. At least two tickets, no way you can reserve them all in one go.
Brussels - Budapest by car: around 13 hours