I've tried a dozen or so... There not to bad and after you've been a few times it gets much cheaper. A typical one is Virgina Hotel next the MK MTR exit D3. Just walk through the little shoe shop to the elevator - 2nd floor.
Regular rate when I started going there was about $120 for 2hrs, last time was about $80 for 2hrs... Yeah, been there a few times
If no available rooms (it does happen) just walk around and find another hotel. You can ask to see the room first before you pay anything. Only rejected a room once because the aircon was not working...