$1000 plus materials and longarming. That should end that discussion. If not, they must really want the quilt.
Seriously though, most people don't have a clue as to how much time and materials go into making a quilt. And Hunter's Star is not a quick and easy one. I wouldn't spend too much time on an estimate until I knew they were serious. Figure out how many yards of fabric, the price per yard you expect to pay, add in batting and backing, and tell them that's just for the materials. If that doesn't end the conversation, figure your time roughly at a wage that makes you feel that you're being compensated for your time and add that. If the quilt needs to go to a longarmer, figure that in too. Don't give a low-ball estimate, and be sure to get half the money up front, with a written agreement as to the full price and when it's due.