To be fair, the ticket price is also paying for the Baltimore Symphony Orchestra to perform. It's not just the Decemberists. That's a lot of musicians to pay, so I expect that's the reason for the high price.
For what it's worth, I'd much rather see Colin perform solo at Iota again or see the Decemberists at Black Cat performing "The Tain" in its entirety for ~$15 again than pay $82 for a performance at Merriweather with the Baltimore Symphony Orchestra, but I don't think that's in the cards.