Do you actually want to make the quilt?
When I get asked to make a quilt that I don't want to do, I quote an outrageous price and timeline, and I tell them that they have to come with me to make the fabric purchases. Usually they don't go much further.
If I actually want to make the quilt, then I spend about 20 minutes and figure out how much fabric, thread, backing and batting I'll need, and the corresponding costs.
Then I figure out how long it will take me, and this is the most important part:
1) how much time to do any design work, if needed
2) how much time to cut out fabrics
3) how much time to sew the blocks/quilt top and applique, if any. I find that I always severely underestimate this, so add an additional 50% onto your time. For instance, if I estimate it will take me 40 hours, then I quote 60 hours.
4) how much time to quilt it.
5) how much time to trim & bind it.
Once you figure out your total time, then multiply that by what you want to get paid per hour. I've made several quilts that have won ribbons, I've been hired to sew several shop examples for some of the local quilt shops.
So I consider myself quite skilled, experienced, and educated, and I refuse to pay myself minimum wage.