I have a longarm for my own use, I don't do other people's quilts. I think the $90 price is about right, considering the time and effort involved in putting a quilt on the frame, stippeling a quilt, the costs of materials, her time planning with the customer etc. I do my own because I know what it costs to have them done.
When you pay a profesional quilter you also pay for their skill and the use of the very expensive quilting machine and tools they use. Another thing most people don't give a thought to is the space the longarm machine takes in the quilter's home/studio, these machines are huge. It's not cheap!
Mary