Last time, we master-planned three trips for under $500 (with no sketchy hostel compromises). There are round trip flights on Expedia for around $130-150 (for four-day trips in July). AdvertisementPerfectly Renovated Historic Downtown Home; sleeps up to 4, $213/night at AirbnbPerfectly Renovated Historic Downtown Home. Fresh East End Apartment Walkable to Downtown Portland; sleeps up to 4, $275/night at AirbnbFresh East End Apartment Walkable to Downtown Portland. Round-trip flights on Expedia to Big Sky from July 16-20 are going for around $185.