The standard accommodation along the Mahakam River is pretty basic, see for instance Muara Muntai. In every village you’ll find a losmen or guesthouse which rents a room and charges around 50,000 Rupiahs per person. Some are better, some are worse, and quality seems to change from time to time, but all come with shared bathroom and shared toilet, and none have hot water, neither towels. Some have mosquito nets, others don’t.
After having roughed it in several villages, the only place with a good hotel, en-suite bathroom, hot water, fast internet and AC is the Monita Hotel in Melak, some 10 —15 minutes walk or a short ojek ride inland from the river front. Definitely worth it, for the 300,000 Rupiahs per room, or so. And very helpful owners, who can arrange cars and visits to the nearby orchid garden and some of the longhouses.