We study the situation of a decision-maker who aims to encourage the players of an evolutionary game theoretic system to follow certain desired behaviours. To do so, she can interfere in the system to reward her preferred behaviour patterns. However, this action requires certain cost (e.g., resource consumption). Given this, her main goal is to maintain an efficient trade-off between achieving the desired system status and minimising the total cost spent. Our initial numerical results reveal interesting observations, which in fact imply that further investigations in the future are required.