You're welcome
The term "IBM Mainframe Administrator" is not one with which i'm familiar. . . It may be the new "in" term
For years much of this administration was performed by "system programmers". I guess "system programmer" has fallen from favor.
There are multiple kinds of administration on a typical mainframe and rarely does one person do all of the admin (like on UNIX or Windows environments). There are several complete administration disciplines like Storage Management, Capacity Planning, CICS, Network, Database, Performance Measurement, Operating System, Compilers and Utilities, COOP (Continuation of Operations Plan - i.e. disaster recovery), Security and more. Sometimes some of these responsibilities are combined in a person and sometimes they are their own group of several people.
I have not been able to find an average salary range
The salaries vary greatly depending on the organization and the availability of qualified people. I've seen wildly different salaries around the country and sometimes even within the same organization (which is why so many places insist that people not talk about what they are paid).
I believe that is because they are much less common than your network engineer, generic server administrator and such
Yes, less common and need far more understanding of the system components. Windows servers are meant to be run out of the box by "newbies" - our dentist is also the sysadm for the complex where the office is located. Unfortunately, he does a better job than quite a few Windows-certified people i've seen escorted out as total incompetents.
I believe 6 figures is quite possible in Dallas. Maybe not right away, but surely possible.
FWIW - i've been a migrant data worker since 1986 so i've seen lots of environments and many people are more willing to talk with an outsider.