There are many reasons why you might be quoted a different price for the same dental treatment. You can always ask your dentist to explain the pricing behind a treatment and should never agree to anything that you do not feel comfortable with.
Dentists factor in the time required for a treatment. This is often why practices provide a range of prices rather than a single set fee. The same treatment for one patient might be more complex than for another patient.
For example, you might have noticed that crowns are often priced from a certain amount. This is because some patients might need the tooth restored before the crown can be fitted. Alternatively, some patients might need less work done to fit the crown. Dentists factor in these differences when pricing a treatment and are unlikely to commit to a final price until they have seen your mouth.