I'm a long arm quilter not far from the Happy Crafter in Kansas. She is somehow able to undercut most other long armers in the area. Not sure how, but she does(she also runs a fabric store so perhaps that pays the bills).
most of us in this area charge 1.5cent/sq in for a basic panto or E2E, 2 +cents for border to border with borders done differently; 2.5 and up for custom. That does not include bat or backing, or trimming/squaring. unless you have a computer guided machine, a queen, even with a fairly simple panto is going to take about 5 hrs loading to unloading. Plus your bat/back/thread. Hope you look at that $100 as not a huge amount when you figure the time, the materials, wear and tear on an extremely expensive machine, electricity to run it, having a place to set up such a large machine, and the quilters expertise.
As a couple of others have said, some long arm quilters are switching to per hour prices, especially on custom quilting, because many long arm quilters, when they figured their costs plus labor realize that they are working for way less than minimum wage.