Isn't 40 hours the minimum? Look for "dual time" on most flight school website then times by 40 to get a rough idea. Of course it will be higher than that with other costs etc, but that should be a general guide.

Always pay as you go, even if they offer a discount for paying upfront, because these businesses are notoriously shaky. Don't hesitate to switch if you're unhappy, most of these instructors are newly minted pilots trying to get flight time, and could be (somewhat) indifferent to your progress.