How much money for a design

Having taught a lot of students studying photoshop, corel, Ai. And when they work, they ask me how much it costs for a design, such as a logo or poster. Please share with some new entrants, new freelancers as follows.

Problem 1: When you value a product, it usually follows a common ground. Look at the person next to you to give the price (lower than the people).
Problem 2: You guys often compare with your working day at the company.
Problem 3: You guys go on “unlucky” when you are high and low.

Please … according to our experience, customers will follow the following formula:
[Experience] + [Working time] + [Device + technology] + [Visitor object] + [discount + relationship] = design price.