The GDK for Unity uses SpatialOS core technology and cloud hosting. This means that when you use the GDK, you need to consider the SpatialOS pricing model.
SpatialOS has a free tier and a paid tier, and you can use the GDK on either of these. For an introduction to the pricing model, see Pricing introduction.
For more details, including information about what the free tier includes, an in-depth explanation of how we calculate prices, and examples of how much different types of games would cost, see Pricing details.