The cost of Dynamics certification varies depending on the exam you take. The exams are offered by Pearson Vue and the prices when this FAQ is drafted are as follows:
Dynamics 365 Fundamentals: $99
Dynamics 365 Sales: $165
Dynamics 365 Customer Service: $165
Dynamics 365 Marketing: $165
Dynamics 365 Project Service Automation: $165
Dynamics 365 Field Service: $165
Dynamics 365 Power Platform: $195
You can also purchase bundles of exams, which can save you money. For example, the Microsoft Dynamics 365 Fundamentals, Sales, Customer Service, and Marketing bundle costs $495.