There is an abundance of places to stay in the area - ranging from expensive air conditioned villas on Railay beach to wooden shacks with palm leaves for a roof on Ton Sai. If you're heading out at peak time it may be wise to book - though you'll pay more for it - otherwise you may end up a 20 minute walk from the beach, up in the jungle where the mozzies, etc are far more of a problem. Arrive out of season and you'll easily just find somewhere to stay by looking around. It's best not to be lazy with this - whilst the places on the beach are very convenient you don't tend to get much for your money. A five minute walk up the main track and you can find something vastly better. On Ton Sai you can spend as little as £2 per night or as much as £20.