The Associated Press (AP) is reporting that up through April, the current cost of The Hobbit trilogy is around $745 million. This total is for pre-production, principle photography, and post-production for the first two films but not the final 8 months of post-production for The Battle of Five Armies. It also isn't clear if that costs include marketing and distribution costs for the film (which are often not reported as part of the cost in making in the film). The total apparently was part of a financial report that Warner Bros. had to file so they could get around $122 million from New Zealand in a tax incentive plan to film there.
Its hard to make a "judgement" call on the cost of the film since not entirely sure if the cost includes marketing as for a film of this scale, that would be about $100 million for each for the first two films but still its starting to look like the films are costing around $250 million each to make on average rather than the expected $150 to $200 million these large special effects movies tend to cost (for comparison, each of the Transformers films landed in that range).
Regardless of where the final costs, with or without marketing expenses added, I doubt Warner Bros. is all that concerned considering the first two films have already brought in $1.98 billion at the box office. Once you add home video sales, merchandise, video games, tie-in products and anything else The Hobbit movies related it all equals to one huge windfall for the studio.