Getting a bus from Chiang Mai to Pattaya
The cheapest way to get to Pattaya from Chiang Mai is by bus and the best bus service from Chiang Mai to Pattaya is NakonChai Air. The buses are new the drivers are OK and they have the best track record of any big bus company in Thailand.
The cost of a ticket from Chiang Mai to Pattaya is 725 baht, for that you get a smaller bus that travels faster than a bigger bus and the trip down will take 11 hours exactly. It's better to travel at night when it's not as hot but sleeping on the bus you may have some trouble well at least for me anyway, I don't sleep well on buses but hate going during the day as well. The Nakhon Chai air buses are the most comfortable I've ever been on anywhere in the world.
To get a ticket for NakonChai Air in Chiang Mai you can go to the bus terminal which you could simply ask a red bus or Tuk Tuk to take you to "Arcade". Arcade is the name of the bus station in Chiang Mai that has buses to Bangkok. There is now a new terminal at Arcade but you don't want to go to the new terminal you want to go to the old terminal in the back next to 7/11 is the Nakon Chai Air terminal and ticket office.
They have buses that go to Pattaya from Chiang Mai every 30 minutes to an hour and the last bus leaves at 7:30. You will need to book the bus in advance about 3 days if you want to leave at that time. If you leave at 7pm you'll get to Pattaya at 6am. If you plan to leave on a public holiday you'll need to book your ticket a week in advance.
You don't have to go to the bus station to get a ticket from Chiang Mai to Pattaya either this is the best thing about NCA you can actually call the call center on 02360009 they have English as well. Call that number and go through the English prompts you'll get a lady on the phone tell her what day your leaving and what time you want to leave. She'll take your name and phone number and give you a number. Write down the number and within 30 minutes walk into any 7 eleven and give them the number and pay the fee, there is a 10 baht fee to do so. This will save you heaps of time, it's best to just stand in front of 7/11 when you make the call then walk in straight away and pay. Keep the receipt though in case you have any problems which is extremely unlikely.
NakhonChai Air website is only in Thai but the call center speaks English. The Nakon Chai Air website is http://www.nca.co.th
Of Course NakhonChai air doesn't just go to Pattaya they have regular buses that go to most places in central region of Thailand. In fact the Air has one of the best and fastest bus services to Bangkok their VIP bus which leaves Chiang Mai at 10:30pm arrives in Bangkok at 6-7am and for 809 baht you get a massage chair your own private tv screen with videos on deman and a sega game console so you can play sonic the hedgehog all night! Actually the VIP bus service to Bangkok beets most airplanes I've ever been on. For those who hate flying like I do the bus is the best way to go.