Fair market value is decided by what equivalent products have sold for within a reasonable length of time.
So research quilts of a like design, using equivalent materials, and of equal workmanship. See what they are selling for and price yours accordingly.
What will increase the price of a product is if it can be classed as art. Then it will depend on how well known the artist is. And what awards the product have won as mentioned earlier. If you want to go into this catagory the easiest way is to hire a publist.