When you install the Shopify integration into Zendesk Support, you'll always have a free 14-day trial. If you don't like it, you can just uninstall it within the 14 days and you won't be billed.

If you decide to continue, you'll get billed once every month. The price is 5$ pr. month, pr. agent. 

You only pay for the agents who have access to this app. So if you've restricted the use of the app to a certain group of agents, you'll only pay for that group of agents.

For instance, if you have 10 agents in Zendesk, but only 4 of them should've access to the app. Create a group in Zendesk and restrict the use of the app to that group.