Boise Airport: The good transfer is Valley Regional Transit Route 3 Vista: it is the frequent, direct airport–downtown bus (about every 15 minutes at peak), roughly 12 minutes to the Grove/central downtown area, for about $1.50. Routes 2 and 20 also serve the airport but are less useful for most visitors. A rideshare is reasonable when carrying bags or arriving late—downtown is only about 10 minutes away, typically around $13 before tip—not an expensive private shuttle.
Boise Airport Bus Stop (regional coaches): Boise has no intercity rail station. Greyhound/FlixBus, Salt Lake Express and Northwestern Stage Lines use the airport’s outer arrivals curb as the practical long-distance bus station; confirm the precise boarding point on the ticket, since some services also use an Orchard Street stop. From there, take Route 3 or a short rideshare into downtown.