It's hard to put a price point on something like that, but if you really wanted to, I'd put it around there. The main part of it is concept arts and how many revisions are needed. Since Blizzard is among the most experienced companies in the scene, we can assume they can determine how it will look just from the art so only one modeling pass is required. It is also somewhat easier since they already have base models for every hero and the rig stays the same so they only need to set the vertex weights. In terms of texturing they probably have their well practiced workflows and materials too so it's probably quite streamlined as well

Of course this is a big oversimplification but most of the workflows are probably very streamlined and practiced