Procurement cost. And to be exact - powerplant still constitutes a significant part of the price(double digits).Cost of the two ships isn't primarily with the engines but on the other systems. 052D still uses two diesel engines and a more complex gearbox to deal with two different kinds of engines.
But when we go to operation costs(and logistics load) - powerplant becomes of huge importance - the more active ship is, the costlier it gets.
That's assuming 052D can't do the same networking(or there is no 055 in TG).But PLAN is willing to spend for it because it is claimed, a 055 is 3X to 4X more combat effective or has greater combat potential over a 052D. I would attribute these combat multipliers due to not just the 055's radar set up, but it has a more advanced CEC, IFF, and the next generation electronic warfare kit. Having this too, will give the hypothetical 052E a combat multiplier advantage over the 052D, especially when the CEC of the 052E and the 055 is networked together.
Given that 052Ds are very recent ships, and their radar/cooperative engagement/battle management system development schedule proceeded at least partially in parallel with 055 - why such an assumption?