Lots of folks come to Pai from Chiang Mai on a bus or minivan. The ticket is 150 baht and the bus ride is around 3.5 hours. Once you get to the Pai bus station, just walk over to Wat Klang and take a left into a little path between the temple and 7-11. This path is right across from the Maehongson Provincial Court Pai Branch. You'll spot Pai In The Sky Hostel there. It's less than a minute's walk from the bus stop.