It is worth what one is willing to pay for it? If this person has said cost is no issue simply present her with an invoice with the cost and if you so desire break it down into where the money is going or not and than let her decide.
I don't think $800 is to much considering all the work that goes into making such an item.
I've seen king size quilts go much higher than that.
As a quilter "you pay yourself" what you feel your time is worth plus materials and such.
Carol