the end of cheap plane tickets

I've been driving myself crazy this week trying to find plane tickets to Denver for less than $350. One of my good friends lives in Colorado and we're hoping to go visit her and her boyfriend for a few days and then spend a few more days seeing some other places in the area. I guess maybe Colorado is just the place to be in the summer, but I was hoping it wouldn't be that expensive. When D. and I flew to see each other during college (a similar distance), tickets were under $180 nine times out of ten. Another factor buoying my hopes was that after a week looking at $330 tickets to Boston (for another trip this summer), I found some for $160. Fingers were crossed that the same thing would happen for Denver, but it doesn't look like I'm going to get that lucky twice. I guess the ever upwards creep of gas prices means that plane tickets aren't likely to ever be that cheap again.