Now that Sunfire is weaker, it needs a cost reduction*
*unless they're planning on giving back some of its lane phase strength
Traditionally, it's had a slightly lower cost because tanks have a more difficult time getting gold during the lane phase. But due to the addition of Courage and Grasp, tanks had it too easy buying just Sunfire cape and so the cost was increased to 2900. Which was all well and good until both of those masteries were weakened.
Now, the item has been nerfed as well. Due to the switch of 75 HP to 10 Armor, penetration items are more effective than before. And the reduction in damage to champions further decreased a tank's chance of coming out of lane phase with a lead.
Black cleaver, a staple against tanks, has 100% gold efficiency without counting its two passives. Sunfire has only 80%, and a weaker passive. Cleaver gives around 3400g worth of power while Sunfire gives only around 2400g. So the difference in cost isn't 200 in Sunfire's favor-- it's about 600 in Cleaver's. And those champions who buy it are designed to get more kills early while the tanks are not. And the "nerf" to cleaver was not to reduce its effectiveness-- it only serves to make the item shred just as much armor as before. 24% of 60 is 14.4. 30% of 50 was 15. If the had not reduced cleaver's shred, it would've been 20 armor.
Sunfire should have its cost reduced, if no other changes are in store to compensate for the damage it's done to melee-range tanks.
- As a side not, the ~580 difference in gold efficiency is close to the 530 gold cost of 20% CDR. So perhaps Cleaver needs it removed or Sunfire needs it added.