I'd like to amend my answer from $1200 to $1400 since the background is pieced as well.
When folks commission a quilt, they know they're asking for a unique item. This is different than someone who just by the way knows you make quilts and asks you to "make me one!" The latter has no idea the time, effort, special-ness that goes into it. The former is expecting a masterpiece. And, they do not think it's out-of-line to pay an artist for their expertise.
Eddie, I know you are not dealing with a friend/customer of the Wal-Mart mentality. And I'm sure they have the utmost respect for you and your work. Quote what you feel is fair to you and to them (I know w/the $1200 you're making less than $4/hr....sometimes that is ok if you get paid partially in dividends from the experience).
Folks that are saying $400-$600? I'm so sorry you live in a climate where that's all a quilt is "worth". I would rather keep it in my home for years and years to enjoy its beauty for myself than to work sweatshop labor on something so lovely.
And Pottery Barn does have some cute styles. They are pricing for the masses and control their costs by buying en masse. Which is ok, if you're into that sort of thing. Obviously this customer is not, otherwise she would have bought one AT Pottery Barn.