I helped an Accounting application that is a SAAS solution to migrate their database from on-premises to Azure SQL Database. They track attendance for small companies same as the application you mentioned. Initially their databases were migrated to Azure SQL VM (IaaS), no issues in terms of performance, but the costs of licensing the OS and the SQL Server Enterprise Edition was huge. From the beginning Management of the organization was aiming Azure as a way of getting rid of licensing costs, and we are talking about dozens of thousands of dollars.
We then merged all databases of the application on one database with different schemas and migrated later just one database to Azure SQL (DTU-model) with no licensing costs. Azure SQL Database provided key SQL Server Enterprise features like partitioned indexes as part of its offering, no additional costs. Azure SQL offers also artificial intelligence at not cost (Automatic tuning, forces the best query plan, creates indexes automatically), high availability, geo and zone redundancy at no cost or low cost. We also were able to scale up reserved database resources during business hours, and scale down reserved database resources during nights and weekends, while still offering 24x7 service to all customers. QA/Test environments were saving by using Serverless database servers that auto-paused themselves when they are not in used. In summary, Management saved more than 45K per year by moving databases to Azure SQL PaaS but moving to PaaS database offerings involved some architectural adjustments.
Azure Elastic Pools can help you keep those 100 databases on a pool and save even more, but if cross database queries are needed you may need to consider using elastic queries or consolidate on one single database.
Here you will find documentation to help you decide.