You can read about the pricing here: https://cloud.google.com/vision/#cloud-vision-api-pricing.

Example: If you apply face detection and label detection to the same image, each feature will be billed individually. You will be billed for 1 unit (1 API call) of label detection and 1 unit of face detection, at the price dictated by your monthly unit volume. If you use 4,300 units in a month of face detection, you will be billed as follows. You will be charged $0 for the first 1,000 units and for the remaining 3,300 units, you will be charged at $1.50 for every 1,000 units, rounded up to the next 1,000. So that would be 4 * $ 1.50 = $ 6. This should give you an idea of how you can keep an eye on your expenses.

 Now that we know the basics of the Vision API and understand the pricing model, let's get started with a hands-on exploration. Before we get started, we need to set up the required authentication and authorization. In the next section, we are going to look at that.