This is a small airline, and as far as I know only operates MD-80 family machines, but they have a fairly extensive reach across the country.
The Fort Collins/Loveland Municipal Airport is a very small facility. It is used mostly for private planes, and over the years had very limited service by Mesa Airlines. A better facility was never in the works because Fort Collins is just too close to Denver International Airport (about an hour and a half away on I-25). However, an hour and a half means a lot when you have to be at the airport at 6:00 a.m. or if you won't arrive until 10:30 p.m. Am I right, folks?
Eventually, Frontier should look into operating out of this airport. The Fort Collins/Loveland area's population is close to 200,000 by now. And if you add Windsor, CO, Greeley, CO, Wellington, CO, Cheyenne, WY and Laramie, WY, which are all closer to Fort Collins/Loveland Municipal than to Denver International, the airline could be serving a market of over 350,000 people with no competition. I would bet that folks would pay a premium to fly out of Fort Collins and avoid the drive to Denver.
They could start with a flight to midwestern hubs, like Chicago or St. Louis. Then maybe start heading south to Dallas. It doesn't really matter where they connect to - the point is that they should JUST DO IT!
Allegiant is a good start. The city has a vibrant college population (of course, I wouldn't know because I lived at home during my undergrad years, but I heard some things that people did and they sounded vibrant). Vibrant people would seemingly be very attracted to the sinful activity that Las Vegas offers - especially for a short weekend getaway.
Imagine heading out to Vegas on Thursday AFTER your last class of the week. Then, after gambling, drinking, and enjoying the other cultural offerings of Sin City, said college students could get on a plane, land, and be home in 10 minutes and proceed to pass out on their couch/futon/whatever hungover college kids are passing out on these days.
Then, they can go to class on Monday and take the midterm.
See ... everybody wins.