To some degree, costs are probably inflated, though. There was a fairly infamous example a few years back - the Tomb Raider movie, where IIRC because of a lawsuit the production accounts were brought into public view, so inevitably they were picked apart by those interested in such things.
Long story short: Paramount's "$94 million" budget, thanks to various international tax breaks, merchandising deals and the like, was actually more like $7
million. Read more here
. Of course, from a studio accounting point of view, that $94 million was almost certainly the 'official' figure when it came to dishing out net, rather than gross, profits.