Talk:Rabadon's Deathcap/@comment-98.211.151.206-20120706092829/@comment-4061583-20121024013335

It is cost effective, IMO.

Deathcap (minus passive) 25.7g per AP

Zhonya's Hourglass: 31g per AP

Rod of Ages (Fully Stacked): 37.9g per AP

RoA (No Stacks): 50.58g per AP

Rylai's: 38.8g per AP

Sounds pretty cost efficient to me, especially as it also helps out with AP cost efficiency of other items.