The City Inn had a reasonable Double Room with hot water ensuite, aircon, wardrobe, and local Malay TV channels for MYR69.
The ‘place to be’ is in the area near the Old Jetty in and around the Borneo Global Sipadan Backpackers. You pay a bit more in this area (around MYR100 for a worse to similar Double) but there are more restaurants, bars, and Travel Agents to choose from.
In the end, I walked back to City Inn and took the Double Room.
Semporna is so small you can walk anywhere in 5 minutes; so, the City Inn's 'fringe-of-centre' location was not a worry (and the hotel was quieter than others).