Managed SQL Server support is a fixed monthly fee for the ongoing administration of your SQL Server estate — monitoring, patching, backup verification, tuning and incident response — instead of hiring and covering a DBA yourself. Onsys plans start at $1,500 a month excluding GST for up to ten instances, which is $150 per instance.
Divide before you compare
A plan at $999 a month covering 3 instances is $333 each. Plan A at $1,500 covering 10 is $150 each. The bigger headline number is less than half the price per instance.

