Welcome to the board.
I have never hand quilted a piece someone else, and I never will. Too much work.
But my husband's grandmother lived in a retirement community for over 30 years(!). She was the head of the quilting group. Since there were numerous women who worked on every quilt at some point, their price was determined by a flat rate plus so much per yard of thread. I think at the time when we were married (25+ years ago) the base cost was $50, plus the cost of the thread, which I think was around 15 cents a yard.
Hope this help.