Indeed, holiday tickets were $650.
Ivona, while $400 tickets are still available (and they seem to be) fewer people will want $600 tickets. That they cost so much initially doesn't matter to buyers; a competitive price does.
If they are physical tickets, a local might be particularly interested in them, because hard tickets require less trust than buying Will Call tickets and having the name transferred. So you might also visit the "Regionals" link on the top right of the main Burning Man website, join some email lists for folks near you (if any) and post that you have holiday tickets. Be prepared to come down in price for the best chance of selling them.
*** 2013 Survival Guide ***
"I must've lost it when I was twerking at the trash fence." -- BBadger
"Snark away, ePlaya, you magnificent bastards." -- McStrangle