You can add an unlimited number of orgs with your subscription.
Gearset is priced at a flat fee per month. We don't believe in difficult to understand or variable usage pricing. The price you see on the website is the price you pay.
You can add as many of your developer, sandbox or production Salesforce orgs without worrying about hidden costs or usage based credits. There are no extra charges or limits on the number of deployments you can run or the number of automation jobs you can create.