If the woman hasn't seen some of you quilts, I recommend you showing her pictures of some of your finished quilts. If she's willing to pay for a quilt after seeing some of your quilts (which I'm sure she would, or she wouldn't have asked you to make quilts for her kids), then give you a good idea of what the cost of the materials would be as well as an amount for your time. I can't tell you a good price, as I think it varies according to the fabrics and the design of the quilt; something like a 9-patch, D9P, or other simpler blocks would not be as much as a more complicated quilt. I wish there was an exact formula for how to price your quilts, but I don't have one.