You will need to keep the poly's down naturally.Best bet for a rope could be simply a taper deformed tube (not to many segments) and a bit of extrusion off the top faces, make it fat for the first extrusion and get thinner for the rest of the rope to the top of your gallows,this requires a nice texture to make it look good.There is of course more than one way to skin a cat and I am sure somebody will come up with a better method than this.You could even use a fixed decal.
Good luck,would it be possible to see a wireframe view of your mesh.
I did make a gallows for an animated music video some time ago but for that kind of thing I didn't have to worry about the poly count.
P.s. You probably dont need the strut you have running down the middle of your stairs.