I often include the story of the quilt - why I selected this pattern for them, what I thought of during the making, how to care for the quilt. But I have never included the price of the materials or what I would value it at.
On the other hand, it *would* be good advice to make sure that they are aware, in some way, that the quilt is not a $20 mass produced item. If it is an heirloom and/or needs to be insured, maybe a gentle suggestion to that effect. If you're really serious, then you could get an official appraisal and include that for them!