Getting There and Cost
It's easy to get to Doi Inthanon from Chiang Mai and well signposted all the way. Head south on Highway 108 for about 60 kilometers. At the town of Chum Thong, you turn right. You'll carry on on a much quieter road for about 10 kilometers until you come across the entrance to the park. Entrance is 200 baht for foreigners (100 baht children under about 12) and about 30 baht for Thais. The ticket is valid as long as you don't exit so you can stay for days...weeks!
Many go by organised trips in fast minivans booked from one of the many (perhaps hundreds!) of tour agents in Chiang Mai. If you're concerned as to exactly where, a laid back street to book would be from one of the agencies on Ratchapakhinai Road (see map). I can't remember charges exactly