I visited Sukhothai as a day trip from Bangkok. Bangkok Airways offers 2 daily flights making it easy to fly in, visit and fly out the same day. I paid about USD 100 for the return trip. The morning flight arrives 8:15 am. The airline offers a shuttle bus to and from the historical park (600 Baht return fare). For 30 Baht I rented a bike for the day. I would not recommend visiting the site on foot only. The site itself is beautiful. I have nothing to add to the other reviews. I entered the historical park on 9:25 and the bus left for the airport at 3 pm. This was more than enough time to visit all, including the outlying temples.