Recently, I started sending my 13 year-old to stuff like that without me. I make sure he's with friends, has his phone, and knows exactly where to be immediately after the event ends. I drop him and his friends at the venue, while I chill somewhere close by.

Like you said, tickets are expensive these days, and I got tired of paying full price to accompany him to stuff I have zero interest in.
I started last year, at a gaming convention, in a hotel convention center. I was about to pay the $50 admission for myself, and then it hit me. I pulled him and his boys aside and laid down a detailed set of instructions. They went in, and I chilled at a coffee shop, until they called me to pick them up.

It felt like a decent test of his independence and responsibility. He's been to a few events now and everything's gone off without a hitch.