Wearing my killjoy hat here...
A quilt is worth what a buyer is willing to pay for it.
(That's assuming you are referring to its cash value. My parents would definitely tell you the quilt I made for their fiftieth anniversary is priceless - but I doubt they would have paid me $20 per hour for the 200+ hours of hand quilting I put into it!)
Alison-the-Reluctant-Realist