Go Camping at Sam Phraya Beach
You can also go camping right by the beach at Sam Phraya Beach, a beautiful white sand beach located in a secluded area within Sam Roi Yot National Park. The campsite is under a shaded area right by the beach and you will have access to the usual facilities like toilets and showers that you can come to expect from Thai national parks. They also have a restaurant there which is pretty good and cheap.
The beach itself is really nice and wide with some soft sand areas closer to the water and it is very quiet and remote. If you are looking for a quiet place to camp by the beach, Sam Phraya Beach is a great place to be. To camp there, you are going to have to pay the Sam Roi Yot National Park entrance fee which is 200 THB for adult foreigners, 100 THB for children, 40 THB for Thais, and 20 THB for children. You can rent a tent and all the other gear if you need which should cost no more than 300 THB. Make sure you prepare mosquito repellent for the night as well if you plan to camp.