If you are looking for a budget trip then id suggest you go there and look for hotels urself. It would be much cheaper. In phuket, pattaya u donot need to be right infront of the beach(its also expensive), find hotels two lane back and you'll find hotels in the range of 1500rs per night. Also dont go for the brands like i did as essentially u'd be spending most of the time outside. Local hotels are as good as the top notch ones.
Also please be aware that thailand is a place to get scammed easily. Do visit bangkok, chiangmai and Phuket/pattaya. Id prefer Pattaya. Try the local cuisine , not everyone liikes it but if you're going might as well. Pad thai is usually good.
You'll have to land in bangkok and then u can take an arranged cab for the other places. Chiangmai u would want to travel via train.