Check out my easy DIY Tricep pushdown system. Simple to make and effective.  A few eye screws, carribeaners, and pullies.  Grab some 500lb capacity rope and your set.  The carribeaners and pullies are all weight rated above any weight that I would use from a system like this.  The end opposite the handle has another carribeaner that goes around the handle of a dumbell or kettelbell and clips back to the rope.  As with paracord, I always burn the ends of the cut rope to keep it from fraying.