Understanding the billing

You are only charged for the render nodes that work on your project. As long as your project is in the queue and not running, you can increase the priority, and so decrease the rank in the queue, or remove it from the queue.

Basically 1 RC = 1€, however it can be less depending on the discount you can get when buying a refill.

the GHz/h

The cost of a CPU project is based on how many Giga-Hertz per hour (GHz.h) are used to render it and also on the chosen priority.
Each processor has a frequence in GHz which tell you how many operation it can performed in a single second.

Example

A 32 cores Dual Xeon E5 2697A V4 uses 64 threads to render and a clock frequence of 2,60 GHz.
If this server compute for half an hour, the GHz.h used will be: 64 threads x 2,60 GHz x 0,5 h = 83,2 GHz.h.

A project of 150 images calculated for half an hour will use 150 x 83,2 = 12 480 GHz.h.
Thus for this project in CPU-Low, the charge will be then 12480 GHz.h x 0,016 = 199,68 RC.
Whereas in CPU-High-256 priority, the charge will be 12480 x 0,021 = 262,08 RC.

the OB/h

The cost of a GPU project is based on OctaneBench score of the nodes used to compute over rendering time and also on the chosen priority.

Example

A GPU server with 4 GeForce RTX 2080 Ti card has an Ob score of approximately 1400 points (OctaneBench 2020 score).
If this server compute for half an hour, the number of OB/h used will be: 1400 x 0,5 h = 700 OB.h.

A project using 14 Nodes with 4 RTX 2080ti cards to compute 28 images during half an hour will use 28 x 1400 x 0,5 = 19 600 Ob.h.
Thus for this project in GPU-Low, the charge will be then 19600 Ob.h x 0.008 = 156,8 RC.
Whereas in GPU-High-24 priority, the charge will be 19600 x 0.013 = 254,8 RC.