The reason for high prices is not only TM, but also:
(1) The band Coldplay itself, which can choose to lower its cut. Bands do this.
(2) You and the market. If Coldplay sells out its tour, which they will, it sends the message that it can easily sell lawn seats for 45 bucks. Next time around, they might try 55 bucks. Concert attendance is down this year, but until it goes WAY down, ticket prices will not go cheaper.
No offense, I've spent much more to see a show. Who hasn't been ass raped at some point?
Enjoy the band, the 7 dollar pavillion beers, and the $30 low-grade cotton souvenir t-shirt.