It sounds as if you are considering outsourcing your DBA activities, and are trying to determine if their estimate / proposal is a fair one.

A few things to think about:

Almost any outsourcing has a minimum time proposal. It's simply not worth their time to enter into a contract for 2 hours a week. So, if they are proposing 20 hours per server per month, that is probably not out of line.

You should not be comparing the amount of work vs. the time estimate provided. The comparison is how much would a full time employee DBA cost vs. the outsourced DBA.

They should have also provided a "menu" of what they are going to do on an ongoing basis. For example, there may be a 24/7 monitoring department with a 15 minute response time when certain types of events occur. There is some real value to this, and if this what is offered, it is worth a bit more.

Also, you typically do not get a single DBA when you outsource. You get a team of DBA's, each with separate sets of expertise. Again, the comparison needs to be a full time DBA vs. the outsourced DBA. A single DBA cannot be an "expert" on every possible subject that may arise.

Good luck!