Thailand has a plethora of accommodation in every price bracket. Always take a look at the room (or better still several rooms) before agreeing a price. In smaller establishments also do ask for the agreed price in writing to avoid problems during check out.
The best prices (30%-50% off rack rates) for accommodation can be found during Thailand's low season, which is during May - August, which not surprisingly also coincides with the region's monsoon season. The peak season is during December - February.
Guesthouses are usually the cheapest option, costing under 200 baht per night (or less for a dorm bed). This gets you a room with a fan, a squat toilet (often shared) and not much else.
Thai hotels start around 200 baht and go up to around 800 baht. The upper end of this range will be air-conditioned, the lower end will not. The primary difference is that with a hotel room, your bathroom should be private, bed linen and towels should be provided, and there may be a hot shower.
Tourist hotels are generally around 1000 baht and offer the basics for a beach vacation: swimming pool, room service and colour TV.
Thai Boutique hotels, 2000 baht and up have mushroomed during the past few years, they usually provide less number of rooms (usually 10 or less) and a more personalized service. The more recognized of this genre include The Old Bangkok Inn , Chakrabongse Villa both of which have royal connections, and The Aleenta group of hotels which is based in Thailand's Southern beaches.
Business and luxury hotels , 4000 baht and up, offer every modern amenity you can think of and are largely indistinguishable from hotels anywhere else in the world. Some, notably Bangkok's The Oriental, The Sukhothai and The Peninsula are among the world's best hotels. The most luxurious resorts also fall in this price category, with some of the very best and most private adding a zero to the price.