It really depends on the tour, artist, what size venues their playing and production costs. I'd say for standing tickets anything form £15-£60 is fair.
I'm not big on concerts, but because I do not attend them very frequently (and when I do attend a concert it's usually because I absolutely adore the performer), I usually don't mind paying an absurd price for tickets.
$150 for floor seats/GA and cheaper the higher you get.
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That's how much they always charge when major stars come to Australia, I paid that when Rihanna came here last year and I ended up 3 metres from her . It was definitely worth it.
. It was definitely worth it.