I asked to a guy in motorbike a cheap place where to stay i explained i didn't want to spend more than 10 dollars for night.
He took me in this guesthouse, cheap 600 pesos for 2 people (300 each), about 10 dollars for night, You can bargain for 500 pesos... they give You a room with 2 beds, a fan and a toilette outside of the room, room is not so clean so basically we slept inside our sleeping bag :D
but it's just in the middle of El Nido, so you can stay out all night and come back when you want just walking.
It's for backpackers, i mean we don't mind if is cheap and not so clean :D
in El Nido is really difficult to find a good and cheap room, BTW we went to book our tour in agency Lagoon, and i asked if he knows someone that could rent a double room with cheap price and he just went to speak with one of his friend he has an hotel and he gave a nice room, clean with bathroom inside the room just in city center for 800 pesos for 2 people (400 pesos each) approx 8 dollars for person.