What's cheaper? What are going to be doing?
I can't comment on the Pullman as I haven't stayed there and I'm not Gold, so my experiences with Hilton and DT are likely not relevant. Cairns at the moment has a number of constructions under way, which means hotels now are busy and upgrades may not be so forthcoming. I really like the Hilton as it's close to the marina and town. Doubletree has got a lot better of late and I'd suggest you'd likely get a HH floor room there, but just what, I don't know. DT is very close to the new Aquarium.
Sorry for being vague, but you really need comment from a Gold HH stayer for it to be relevant. There is only one hotel that would be likely to prise me away from either of the Hilton properties at the moment and that is the Riley, but that looks too unfinished and too expensive just now (and I do get corporate rates there). To answer your original question, Hilton is not $110/night better than DT. IMHO. Keep in mind that (I think) Pullman is in two parts, the one attached to the Casino and the one across the road. I have heard the one on top of the Casino is the better of the two, but as I said, I haven't stayed there.