here is where i always got tickets for colorado. I dont know if it is any better than what you have found already but it might help. This place is in Idaho Springs its on I 70/76 on your way to summit county from denver so you dont have to go out of the way. It looks like they dont have prices of this season yet.
'No sympathy for the devil; keep that in mind. Buy the ticket, take the ride . . . and if it occasionally gets a little heavier than what you had in mind, well . . . maybe chalk it off to forced consciousness expansion: Tune in, freak out, get beaten.' HST