An LATimes.com blog entry discusses why you can almost never trust most reports of film budgets.
Investors, at least, should be getting accurate info. But “studio math” is notorious, as some people involved may get paid more based on how much money a film makes – but gross and net are two very different things! Executives and producers and even directors may want to portray themselves as having kept costs down, while the marketing folks might think touting the high expense of a film may draw a larger audience. Talent agents want to portray their clients as generating much more money than they cost. And what gets included in the cost of the film, beyond production/distribution and marketing? Research and development that could also be used in other projects? New facilities built by the studio?
You get the idea. There are lies, damned lies, statistics, and studio math.