I've been thinking about how the venue effects the cost. Our shed seats 18.5 and AAC (where the Stars and Mavericks play) is a fancy-ass arena with 21k seats. Shows at the AAC are always the top tier acts, Madonna, Metallica, U2, etc., and always sell well. A lot of the bands I'll see play Starplex. That's where Maiden and Rush (before this tour) always play, along with all of your package type shows. Since the lawn almost never sells out, it's pretty common to see them selling those seats for $20 the week of the show. Since there are often dirt cheap lawn seats for sale, that lowers the cost of everything else accordingly.
I suppose the moral of the story is that if you know for a fact you're going to sell 21000 seats, then why wouldn't you sell them for as much as you can get? Those are the shows that play the nicest, newest venues. If you know you've got more seats than fans in a market, you play cheaper digs and make your tickets more affordable to the masses.
As an aside, Roger Waters was the most expensive show I've seen. Lowers for the Dallas show were $125+TTL. We paid $200 for 10th row center in Tulsa. My thought at the time was that while I'd prefer to not have to spend that much money, the fact is that if anybody deserves it more than Roger, I'm not sure who it would be. Given the insane amount of enjoyment and pleasure the man's brought to me over the years, I consider the $350 he's gotten out of me this decade to be fine price to pay.