Speaking from my own experience...everyone's mileage will vary.
My Newfs as puppies ate considerably more than they did as adults. Where my pups would eat from 4 to 6 cups of food a day split into three meals, as adults they ate 2 rounded cups per day, split into 2 meals (one rounded cup per meal). I feed Taste of the Wild (rotating the protein source with each bag) and a 15 lb bag, at $33.00 US, lasts one adult dog nearly a month, so a puppy is roughly double that amount. But I also give plenty of very tiny treats when training, so you need to factor that in as well.
Puppies eat a lot until they are around 7 to 12 months and then they don't seem to want or need that much food any more. If fact, they will often tell you they aren't that hungry at certain stage. So if you can hold out cost wise until then, you might be pleasantly surprised.
The biggest thing to consider is that you want them to grow slowly and then remain lean and muscular all their lives. It's far too easy to overfeed a Newf. We often tend to overfeed thinking it will make them grow bigger, but the emphasis should be on keeping them thin and healthy rather than big and heavy. You shouldn't try to make a dog grow bigger than he is genetically programmed to grow. Trying to do so, will only cause health problems. You can get a rough estimate of his adult size by looking at his relatives. Not just the parents, but the siblings and grand parents, too, if possible.
Newf weights vary greatly. So a trim and healthy 120 lb male is far more desirable than an overweight 160 lb male and will be less likely to develop health issues, especially orthopedic ones. Be sure you are familiar with the standards for the breed (especially structure), and also learn to recognize when a dog is overweight or lean. The numbers on the scale are not as important as getting your hands on a dog and feeling his ribs. If you can, go to any dog shows in your area to get an idea of what a Newf should look and feel like as far as weight goes. Talk to the handlers (after they've shown in the ring) about feeding and ask them if they will show you how to check for healthy weight on their dogs. Or ask your vet. DO NOT RELY on what the dog food bag suggests for amounts to feed. It's very, very wrong. Each dog is an individual whose food should be adjusted to him, not what some marketing person decides.
As an aside, it's funny that when people (non Newf owners) look at my dogs, they estimate their weight to be anywhere from 200 to 300 lbs and think they eat 8 cups per day. Seriously! When I tell them my dog weighs 125 lbs and eats 2 cups, they are astonished. Newfs don't need to be huge in order to be impressive.
Feeding a quality adult food is paramount to health, so look at prices on premium foods in your area. I believe you will substantially lengthen your dog's life if you feed good food and keep him reasonably active. All my Newfs have lived well over 11 years with the oldest one being just shy of 14. He was active all his life and ate the best (not the most expensive) premium food which I felt I could afford.
My sermon for the day:
Make sure you are buying from a quality breeder who emphasizes health and working ability over size. If the breeder continually boasts about how large their dogs are, consider that a red flag. And if they tell you they have never had health issues in their lines of dogs, then run like all hell broke loose. Also find out if they show their dogs or their dogs participate in working events or other activities. Even if you have no desire to show or work your dog, Newfs are meant to be active to a certain degree, though we think of them as couch potatoes most of the time. They can't be athletes in the sense of jogging partners, but should be able to do the work they are bred to do. Strong, steady workers.
There are plenty of threads in this forum on selecting responsible breeders, so spend some time reading those and learning what to look for in a breeder.
In any event, just remember, bigger is not always better. If you are going to err, do so by feeding slightly less rather than over feeding.
Best of luck in your decision making.