Time and Distance Are Money
The farther you fly, the more it's going to cost you. The farther your arrival airport is from Glacier National Park, the more it's going to cost you. The smaller your arrival airport is, the more it's going to cost you. On the other hand, as long as your arrival airport is west of the high plains, there will be absolutely no shortage of scenic roads between it and Glacier. And as long as your arrival airport is within two easy driving days of Glacier, you will have plenty of time for the drive to and from the park as well as a few days in the park itself.
With all of those thoughts in mind, there are several arrival airports that would work for you. The nearest major airport would be Seattle, followed closely by Portland and Salt Lake City. Slightly farther away, but still within reason, would be Denver. Any of those four cities could work for you. So the first thing you'll want to do is to check flight availability and cost into those four airports, as well as car rental rates. remember that it's the combination of those two factors which will largely determine the total cost of your trip.
No matter which airport you choose to fly into, you will have a scenic drive to Glacier with sites to visit along the way. From Seattle or Portland you'll be crossing the Cascades, the Palouse, and the Bitterroots. From Salt Lake city you'll traverse the Great Salt Lake Basin, the Snake River Plain, and the Big and Little Belt Mountains. From Denver you'll see the Front Range, the Great Divide Basin and the Wind River Range. Salt Lake City and Denver would also offer you the chance to at least drive through Yellowstone National Park as well.
So have a look at those four airports for costs and general suitability to your own goals. Once you've decided on one of them we can give you more detailed suggestions for routes and sights to see on your drive. But rest assured, you can't make a bad choice.
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