There are several kinds of bike for rent at different prices. The cheapest of all the town, which is the one we took, is a simple automatic that costs 100 baht every 24 hours. Yes, every 24 hours, so if you take it today at noon you should not give it back at night before they close but the next day at the same time.
When renting it, the procedure is very quick and easy, you just have to choose the model you want, fill out a paper, leave your passport and get on the bike to begin the adventure. You can buy third-party insurance or go without it, or you can also get a helmet leaving 100bht as deposit, that will be refund when you return the bike and the helmet back.
When returning it the procedure was as easy or more than when we took it. We arrived, we showed that the fuel level was the same than before renting it, we gave the helmets back, and they gave us the deposit and the passport and we left.
Of course, if you want to hit some good curves driving for several hours, you can also drive to Chiang Mai and return the bike there, as they also have a store.
So you know, when you go to Pai do not stay several days walking around the town, nor pay the tour which will take you from one place to another without any freedom. Rent a moto at Aya Service and discover the region by yourself getting lost in it.