Chris wrote: "I think they are wanting something simple, like sashing and cornerstones around the blocks, and then a border or two." IMHO I don't think this is 'simple'...simple to me would be sewing the blocks together as they are (no sashing or cornerstones) with one border. Just my humble opinion. Another question - Who's quilting it? How much detail will be applied to those sashings and cornerstones and a border or two? Takes time and money to do that.
I've never had to figure the cost of making a quilt for someone...but IF I did, I would figure out how long it would take me (moving quickly and efficiently) along with the price of materials (and time needed to shop for them). Then I would multiply the hours by an hourly rate (only you can decide) and add price of materials.
Sometimes non quilters will say "Oh you should make one for me!" and my instant reply is "How much do you think I would charge?" Their response is usually nothing or some ridiculous low ball figure.
Since you situation is a serious inquiry into making a quilt for someone, I would figure out
how much I would charge. Then I would ask them
what they 'think' it would cost to have you do it. Point I'm making is IF YOU think it'll cost a reasonable $400 to make the quilt (and it sounds like start to finish (except for the blocks) and they think it'll cost $100
you'll have to be prepared to explain the REAL LABOR TIME and ACTUAL MATERIAL COSTS involved. I would want to know
where they are in their thinking of price before I talked to them about a higher price.
People who don't quilt...don't understand the time and money involved...
People who quilt...understand and are willing to pay if necessary.
Interested to see how this turns out.