If you are going to Denver, have you booked your flight yet?  Thanks to Nick M, I learned about cheap flights on Southwest.com.  They have flights on Wed out and Sat return for $79 / one-way.  On Sunday, they return would be $89 / one-way.  That's still cheap to get a weekend in Denver!

 If you'd prefer something other than Southwest, another cheap flight is Frontier Airlines out of Midway