One MySQL database or many SQL Server databases
If hosting externally is an option, you can get a MSSQL Database on Azure for as little as $5/MO.  http://azure.microsoft.com/en-us/pricing/details/sql-database/

The Basic tier has a 2GB limit, but you can get 250 GB for $15/MO.

Azure plans also come with: 


  built-in backup support, with the ability to point-in-time restore
  your data from any transaction up to 35 days. Additionally you can
  automatically replicate to another Azure region of your choice. This
  enables you to easily implement a disaster recovery policy designed
  for your business needs.


Might be worth checking out for just a few $$ per month.