The airport code for the Denver International Airport is DIA.
A flight comparison site such as Hipmunk is recommended to get an idea of the prices on several airlines (most sites don’t include Southwest Airlines). You can also set up a fare alert from Airfare Watchdog, which will let you know when there’s a good fare to Denver.
United Airlines offers a discount for groups of 10 or more. More information can be found here.
Discounts of up to 10 percent are available for groups of 10 or more traveling together. The discount depends on the type of flight being booked. On the Delta.com website, use code NMKT9.
JetBlue offers its lowest available airfare for groups of 10 or more who book together. More information can be found here.