Here are a few common compensation models to consider for this aspect:
1)Flat Fee arrangement: Under this you and the freelancer agree upon a fixed amount to be paid for the entire project.
2)Commission-Based: Under this the freelancer's compensation is tied directly of generating revenue through the pitch deck.
3)Hourly Rate: Under this the freelancer charges a predetermined rate per hour of work.
When determining the specific terms of the compensation consider factors such as the freelancer's experience, the complexity of the task etc.