Total for our multi-leg flights around Australia for the three of us a few years back came to £5,245.53, but that was Heathrow > Singapore, Singapore > Melbourne, Adelaide > Brisbane, Brisbane > Sydney, Sydney > Melbourne, Melbourne > Singapore, Singapore > Heathrow, so not quite as eye watering as it sounds.
The most I’ve ever paid for a gig was probably Bjork at the Royal Opera House. No idea how much that was but I remember it hurting my wallet A LOT