Most eastbound I-90 travelers press on to Missoula  once they cross into the state, but there are several quite passable lodgings along the interstate. Just west of the state line in the Idaho town of Mullan, the Lookout Motel (208/744-1601, $25–40) has clean, basic rooms with no phones.
Down the road from Lookout, there is a string of small towns with (mostly) small unremarkable motels. You’ll know the town of Haugan is coming well in advance from the many billboards heralding the World Famous 50,000 Silver Dollar Bar (exit 16, 406/678-4242 or 800/531-1968, $50–75). The sprawling Silver Dollar complex has a bar, casino, gift shop, and restaurant at its heart, and it’s a good place to stop for roadside refueling or a break from the road.
The highway-side but still quite woodsy Black Diamond Guest Ranch (121 E. Frontage Rd., 406/678-4000, www.blackdiamondguestranch.com , cabins $50–70) has lodging in 100-year-old cabins (rustic, but with bathrooms and basic kitchens), camping in large canvas-walled tents ($8 per person, showers extra) and RVs ($10–25), and trail rides. Pets are permitted.
In St. Regis, the Super 8 (exit 33, 406/649-2422, $60–80) is a reliable spot that permits pets.
Down the road in Superior, the Budget Host Big Sky Motel (exit 47, 406/822-4831 or 800/283-4678, www.thebigsky.net/budgethost , $48 s, $54 d) has spacious rooms and is a good bet for a pleasant stay.
In downtown Alberton, the Ghost Rails Inn (exit 75 or 77, 406/722-4990 or 888/271-9317, www.ghostrailsinn.com , late March–Dec., $60–90) has been transformed from a funky old wood-frame hotel built in 1909 to house railroad crews into a tidy B&B inn, just down the street from a used-book treasure trove, the Montana Valley Bookstore.
When Missoula’s motels  are booked full, this is a very attractive alternative.