An appraisal is the way to go. I had a wall hanging I made for one of my sons appraised and was surprised when it was valued (insurance appraisal) at over 1,100. Not as large as the quilt you are talking about. It was worth the 45.00 to know my work has improved to that level. When I gave them the quilt the appraisal went with it. That way they can talk to their insurance company to see if they need to insure separately. They already know the time and material that went into it let them know you have value in what you do.