Hi @NNJ
First of all, there is No extra fees outside SQL Server for SSAS.
It depends on what is your main purpose and hardware also.
Azure Analysis Services is an on-cloud service, and SSAS is on premise.
SSAS on-prem could have traditional multidimensional OLAP cube while on Azure Analysis Services we could only have tabular model now.
Azure Analysis Services we could pay as used.
Best regards,
Percy Tang