You can rent an automobile at the airport. Also, the Estes Park Shuttle will take you from your gate at the airport to the door of any address in the Estes Park area (including the YMCA), and will return you from any address to your gate at DIA. They pick up several times per day; see the website for pickup times as they vary by the season. The cost is $85 for round trip, and $45 one way.
Contact: Henry Guy if you need assistance with any sort of transportation issues.