'X-Men: Days of Future Past' recently returned to Montreal for a few weeks of reshoots. This, in and of itself, is not really news as virtually every big-budget Hollywood movie actually sets aside time for reshoots in their original schedule. But, as Fox announced the reshoots, a more interesting note came along with it: 'X-Men: Days of Future Past' is now the second most expensive movie in the 78 years of 20th Century Fox, behind only James Cameron's 'Avatar.'

The news comes from the Calgary Herald, which doesn't cite a source for their numbers, but the article frequently quotes Quebec film commissioner Hans Fraikin, who would likely have some inside knowledge of the numbers. Assuming it's true, how much does this mean 'X-Men: Days of Future Past' actually cost?

'Avatar' was officially listed as costing $237 million, though numerous reports say that number was actually closer to $310 million. If we split the difference, that would mean 'X-Men: Days of Future Past' cost less than $280 million but far more than the $160 million cost of 'X-Men: First Class' and the $120 million of 'The Wolverine.'

It's surprising that Fox would let director Bryan Singer spend so much, especially coming off his last film, 'Jack the Giant Slayer,' a film whose budget rose to over $195 million, but only grossed $65 million.

Where is all the money going? It's likely that with such a massive cast of hot young stars, the cost is going to actors like Hugh Jackman, Michael Fassbender and Jennifer Lawrence (not to mention Patrick Stewart, Sir Ian McKellan, James McAvoy and Halle Berry). Period films are notoriously expensive to shoot and 'X-Men: Days of Future Past' is unique in that it takes place in two periods, neither of which are present day. There's the 'X-Men: First Class' cast in the 1970s and then the original 'X-Men' cast in the alternate future.

The 'X-Men' franchise is Fox's biggest right now and their budgetary gamble might be a sign of confidence (or desperation). Perhaps the Excel spreadsheets are on their sides: the previous most expensive 'X-Men' movie was 'X-Men: The Last Stand,' which also happens to be the most financially successful.

More From ScreenCrush