By bus[edit]
Buses and mini-buses depart from Chiang Mai (Arcade station - tel:053304748) and Mae Hong Son. From Chiang Mai, regular public buses (no a/c) take around 4 hours and charge 78 baht, and there is only one bus at 7am daily (November 2014). The privately-operated mini-buses take around 3 hours. There is a 15 minute rest stop at the small half-way village of Mae Sae, which has very good Northern sausages, seasonal fruits, and traditional curries and soups available as well as snacks, drinks (excellent coffee!) and importantly, free internet & well-serviced toilets {3 baht}. Tickets sold by guest houses and travel agencies cost about 150-180 baht, however the best option is to head straight for the ticket office adjacent to the orange/white mini-vans and buses at the far side of the old Arcade Bus Station (across the road from the new bus station). Tickets are consistently 150 baht here, the buses are well-serviced and fitted with better quality brakes appropriate for the 762 unforgettable curves that carve their way across the mountain range, and even better, you can avoid complications from booking via guest houses (extra cost due to booking commissions; and poorer quality mini-vans that often have non-functioning air conditioning).
If your budget is extremely tight, take the public bus (one daily at 7am, 78 bath, 4 hours). It's not highly recommended as the buses are older and less up to the task of the demanding mountain carriageway, however some travelers prefer the slower pace in order to ease the gravitational pressures of cornering on one's stomach and to take in the scenery. But after traversing this road perhaps a hundred times or more, the orange buses are by far the best option and give you a better chance of getting to Pai in a timely way and unwinding at your guest house.
The buses described above generally operate hourly from Chiang Mai to Mae Hong Son via Pai and services commence from around 06:30 with last service around 17:30. In high-season season those services often increase to half-hourly.
It may also be possible to privately hire a small red pickup truck (known as a songthaew) that can carry up to a dozen people, from the Arcade station, but you would be looking at a minimum cost of around 1,200 baht which doesn't compare with the much safer and economical private mini-bus service. If you choose this option, the view and wind in your face may be pleasant, but not the exhaust fumes, road grime, and seasonal humidity.
TOP TIP: From your guest house in the Old City precinct of Chiang Mai, walk to prominent Thae Pae Gate and flag down a red songthaew and ask "bai arcade satanee rot bat, mai?" ("Do you go to Arcade intercity bus station?). Most but not all, do or will go there and the fee is just 20 baht per person. Tuk-tuks will usually want 150 baht for the same journey. On your return from Pai you will be inundated by pushy tuk-tuk and private hire songthaew operators, but a simple "mai ow krap" ("No thanks", said politely) followed by "tong khan songthaew bai Thae Pae gate" should see you directed to the small flotilla of waiting red songthaews, which involves a wait usually of no more than 10 to 15 minutes to get a shared 20 baht ride and avoid sole chartering at significant extra expense. It it takes too long, watch which direction the songthaew goes (towards the west and the distant Doi (mount) Suthep, and flag one down on the side of the road for 20 baht!they charge extra for returning a bike in a new city after a 1-way trip. They will keep your passport and send it along with any baggage to aYa in Pai.