One main difference appears to be the size of steel to construct it (and amount of bracing, perhaps- look closely at the designs) which relates to wt capacity. As a mechanical engineer, that jumps out first. The other thing I noticed (aside from all the accessories mentioned before) is the inside space of the cage.
3" X 3" X 1/8" Steel Tube Construction–1000 lb. Capacity.
30" from front to rear post (inside)
Doesnt say steel size or wt capacity.
26" Distance between Posts.
Heavy Duty 2 1/2" Sq. Tube Construction–1000 lb. Load Capacity.
26" Distance between Posts
Looking at these factors (and appearence) it appears that the $259 is not built with quite the same steel as the others and has no load capacity listed, which leads me to believe it has a lower capacity. Just how low, I dont know. But do you really need a 1000lb capacity?