I went to a gig last year some time, but had only bought one ticket. My friend travelled with me and planned to buy a ticket outside...and then they asked for £100! We had £40 with us, so we literally couldn't pay that price.
Eventually, the doors opened and we managed to get the ticket for £40. Soon after, just before the main act came on, we found somebody else who had just paid the face value of the ticket. So that's very true, they wait for the show to start and then begin to lower the prices.
We weren't TOO pleased with what we'd paid but...it happens