At one with nature
Jungle Club is proof that you don't need to spend a lot of money to have a nice holiday. Accommodation is in little huts made from wood with dried grass roofs, and feels a world away from the resorts on Samui. There are a few modern conveniences like TV and mini-fridge, but don't expect any air conditioning! Instead the huts have openings to let in the breeze and a fan.
Jungle Club is at the top of a hill and hard to get to (taxis won't take you there), so you'll need to arrange transport with the resort. They can pick you up from Chaweng Beach and offer a free shuttle service there every day if you want to go shopping or eat somewhere different. The restaurant on site is alright, though you'll probably want to bring some snacks (like chips, cookies, etc) if you're going to spend a few days here.
The biggest downside would be that it's far from the beach, but the view from the pool is amazing!