When I was little, as we watched the fighter jets flying down the valleys we used to count 10, 20, 30, 40... more or less the cost in pounds of flying the things, which is currently about £8 per second. Obviously not a training jet, but even these are pretty stupendously expensive to run.
I once met a Tornado pilot who told me that he had done 2000 hours on Tornados - when I pointed out to him that so much flying would cost £60,000,000 he was quite shaken.
So who flies jets as a hobby - training or otherwise? A few names that I've come across are those of the Googleigarchs and the SpaceX founder Elon Musk. So does Larry Ellison, founder of Oracle. Rich people, in a word.