So figuring out that the Otres Beach is a pretty laid-back place it immediately caught my interest. The best way to get there is from Sihanoukville town where you can ask a tuk tuk driver to bring you there. During day time you might pay min. 3 $ but as soon as it gets dark the drivers will charge you min. 5 $. You should always stay resistant when you bargain. It might take time and patience to find a cheap driver but it's not impossible to find one you can easily bargain with.
Otres is just one long road by the beach with bungalows and beach bars on both sides. I recommend to get a bungalow on the beach side of the road. Well, it's not really a road it's just a dirty, stony, sandy path next to the beach. Go further down the road to find cheaper accommodations. A 2-person bungalow varies from 10-30 $. My travel buddy and I stayed at "Chez Paou" in a really nice bungalow right by the beach with a great view by the water. At night we fell asleep to the sound of the waves. The bathrooms outside are shared with the others but they are clean and mentained very well. In one of the showers there's even a huge tree growing. It was an amazing place with a friendly staff, a nice bar and great pool tables. We got a bungalow for 15 $ a night instead of 20 $ because it was low season. It's a bit far from Sihanoukville town so you would need to rent a scooter to get around. And once in a while the electricity cuts off for several minutes, so you have to be aware of total darkness sometimes. It's a great place to stay in Sihanoukville if you want to prevent young backpacker kiddies getting drunk, taking drugs like stupid and sleepless nights in noisy hostels. Otres beach is definitely the most laid back beach in Sihanouville. There're also few travel agencies there which would arrange bus tickets to your next destination.