It's the Producer's job to determine the cost of the film based on the script. An Executive Producer usually just provides part of the money necessary to fund the film, and they provide their support through name recognition in many cases as well.
Basically what you have to do is go through the script and break it down into what locations, objects, props, actors, costumes, visual FX, special, FX, makeup, and all other things that each scene will need. And then you have to do your research. Go online to multiple different hardware stores, makeup shops, costume shops, amazon, ebay, specialty catelogs, and find out the general price of each main item you will need.
It helps to be thorough about it, but your initial break-down of the costs may or may not need to have every single last item broken down into number and cost, a lot of that can be covered by minor over-estimating.
Though, if this is a short film and not a feature length script, I suppose you ought to be itemizing absolutely everything that you can since the script is short enough to do so, and then you can be more accurate with your numbers.
You'll also have to factor in equipment rental costs, storage space rentals, permits, fees and wages for certain crew-members like security and armorers if they are needed, fire-fighters if pyrotechnics are in the script, room-and-board and travel-expenses for actors from out of town (especially if they are known actors), Craft services and other picnic supplies for each day of shooting. And we can't forget cardboard and plastic containers to hold everything, and enough office supplies with pens, markers, pencils, tape, and paper to keep track of everything above as well.
It can obviously become an enormous mountain of stuff to think about. But once you've done it at least once or twice, the stuff that you always need for any project will become a lot easier to factor in first, and then you can focus just on what a specific script needs in addition to the essentials and staple items.
Now, in answer to your question: You can try to find someone who can specifically help you work all of this out, but researching all of these things can be a week-long process, if not longer, and usually you would want the person figuring all of this out to also be the person that actually goes out and make the rentals and purchases so that the numbers stay relatively the same. Because not only should you put down the numbers and prices that you find while researching, but you should also factor in the shipping cost if you buy stuff online, and make sure you save the name of the business so that you can use them later when you actually need to purchase the items on the list.