To trade with a robot you need the robot itself, the settings which we provide when you purchase it and a running machine that runs the MT4 application during the time the markets are open.
You will also pay broker fees, which are taken as a certain value in percentage from your trades. Check with your broker to understand which fees they have.
In this way, the only additional cost which you can have, is hiring a VPS for trading. Check the section about VPSs to find out more information.