You can see the price factor as a tax rate. So for every credit you use you have to pay an x amount of tax rate. This rate depends on your current subscription plan, variable (minimum of x2) for free, x1.6 for Starter and x1.2 for Pro subscriptions.

Example; if you want 10 views for your video and you are on the Starter subscription plan, then the base cost for this campaign is 16 credits, 10 views * price factor of x1.6. If you are on the Pro subscription plan, the base cost for the same campaign is 12 credits, 10 views * price factor of x1.2.