mini ac seems the most logical (but more expensive watt wise). Plenty of other good ideas posted.
Having no windows in the room is a pain (as I'm guessing it takes far longer for the room to cool down from the day temps).
Meaning running at night (say 7 to 7) probably isn't going to have the positive impact on lowering temps.
And I'm guessing there is no way to bore a hole (in one of the walls) to create a vent route.
Most other techniques (other than the ac) would probably be a little 'bodge job'. Buckets of water and ice, sitting behind fans running full tilt
If you're not opposed to it, perhaps try a Cooltube setup. That might help lower the temp a few degrees.