Mandarin Oriental Hotel in Bangkok is commonly voted as the best in the world by travel magazines. The Amanpuri in Phuket is a study in pleasure to the senses. Compared to 5 star hotels in the west, both are bargains.
Thai hotels such as the Banyan Tree Resort have incorporated luxury health spas as an added attraction. Some are pricey while others are reasonable.
Hotel Rack Rate
Thai hotels are bargains when compared to other countries in Southeast Asia. Even at their "rack rate" Thai hotels are competitive. Travel agents, tour operators and internet booking agents get hotel discounts ranging from 20% to 50%.
Hotel Price and Value
Since a hotel room or resort is usually a significant portion of the cost of a holiday, especially in Thailand. So cheaper hotel rooms mean cheaper vacations, or the ability to stay longer. Or it can mean that the traveler can have a much more luxurious hotel or resort room in Thailand than in other countries on their itinerary.
Agents that book Thai hotels are prolific on the internet. Do a search for "Thailand hotel" on Google and you will find more than a dozen .. and thousands of affiliate sites. Many have the same hotels at different prices. Some hotels, especially in the off season will offer promotional rates.
Compare prices, read the fine print about what is or is not included. If you see a price followed by "++", it means that 7% VAT and 10% service charge will be added to your bill. Some hotels include breakfast in the rate, some do not. Sometimes on special holidays such as Christmas and New Year, hotels will have "mandatory" charges for dinner parties, etc. If you have doubts, send an e mail and ask about specifics.