Budget (2014): Most of Thailand is very affordable. As long as you stick mostly to street food, stay in budget hostels, and use public transport $20 per day is entirely possible, with $25 being perfectly adequate. The only exception is the south of the country. Many islands there are very expensive, though those tend to be the ones most unbearably crowded with tourists.
Worth seeing just for the ruins, where numerous Buddha statues sit with lopped-off heads. If you are going to Kanchanburi as well, go there FIRST, as you will have to circle back to Bangkok to get there. There is no train from Ayutthaya to Kanchanburi, but there is easy transport from Kanchanburi to Ayutthaya. Found out the hard way, and ended up just going straight to Chiang Mai.
This is a sprawling, huge city, which is the capital of Thailand. It is very touristy, especially in the Banglamphu and Sukhumvit areas. The former is home to the infamous Khao San Road. I much prefer this area, because it has lots of temples and is easier on the wallet. The latter area is more metropolitan. It has nice hotels, fancy shopping malls and restaurants, and much less to offer in terms of culture. Beware new travelers: Tuk-tuk drivers will try to scam you.
Really nice city in the North. I could see myself living in a place like Chiang Mai. Imagine a smaller, quieter, friendlier cousin of Bangkok's. Seems like a nice place to settle down or retire. Definitely more affordable than Bangkok, and recommended for the more "peaceful" city dwellers.
Really great place. Here you can take a bus to Erawan National Park, which has many beautiful waterfalls. It is also near the River Kwai; please make sure to visit the bridge!
Ko Pha Ngan
I only went here for the Full Moon Party. It was ok. I'm sure there are plenty of nice beaches on this island. If partying is your thing, you will have a blast here. Like most of the South, it is also very expensive.
In my opinion, even more touristy than Bangkok. If you are into expensive, bar-filled tourist traps, you will LOVE this island. Otherwise, skip it and go somewhere quieter
Ko Si Chang
Situated in the Gulf of Thailand, this was one of the highlights of my trip. It is a tiny island, one which you can walk through in about six hours. It was mostly Thai tourists there, and had a very laid back feel to it. It also had killer sea food! The only bad thing is that the dogs tend to be very aggressive there; one of them nipped me pretty hard.
Nakhon Si Thammarat
A really cool city in the South. Possibly my favorite place I visited in Thailand. It felt really different from the rest of the country, both in attitude and culture. People would genuinely smile and wave to you if they passed by. A family even invited us into their home to give us some birthday cake! It's a big city, and I only stayed in the area of Khanom. However, I cannot recommend this place enough.
Another highlight of my trip. If you like nature, I'd recommend spending just a day or two in Chiang Mai, then heading straight to Pai. It is one of the chillest cities I've been to in Thailand, and has many elephant camps. Unfortunately, this is the dark side of Pai. The elephants are not treated well, so play with them all you want, but please don't ride them.