I have a longarm and do quilting for a business. Saturation will depend on the area in which you live. I live in a rural area of southern Missouri. I would not say we are saturated with longarm quilters, but have an over abuntance of "cheap" quilters. Longarm quilters that will do a king size quilt for $40.
The hard part is trying to explain the difference between good longarm quilting and "cheap" longarm quilting. One quilter, in my area, I would love to string up and disable the machine!
This quilter charges $40 for a king size AND provides the batting! They use one panto pattern for all quilts regardless of size. The poly batting is the cheap very lumpy type of batting. The panto pattern is very large so some spaces as large as 7 inches will have not stitching anywhere. These large spaces of no quilting accentuates the lumpy poor quality batt that is used. After 1 washing the quilt looks terrible! I know this personally because my aunt used this quilter ONCE.
Check with the local quilt shops in your area to see how many longarm quilters are listed with them. Talk to other quilters and find out who they use for longarm quilting. This should give you a decent idea of longarmers in the area. Also, find out their charges. Find out what they include in their quilting.
Some longarmers charge a design fee, thread fee, loading fee and the like. I just have a flat rate for different sizes of quilts. I differ from other quilters by offering to apply binding to the quilt free of charge.
Good luck with your research.