Hotel prices in beach areas are generally lower than what you'd pay in Bangkok (Phuket excluded) but higher than in other parts of the country. There are budget bungalows and guesthouses everywhere, though if you haven't booked ahead in high season you may end up in a questionable room with just a humble fan. At the other end of the spectrum are upscale resorts that run more than $1,000-plus a night—though they are some of the most luxurious resorts in the world.
Banks and ATMs are everywhere, and can always be found outside the numerous 7-Eleven stores, but it's still always a good idea to carry some extra cash. Remote islands do not widely accept credit cards, but have many eager currency exchangers. Some places add a small service charge, typically 3%, when you pay with a credit card.