will they be supplying the fabrics for the sashings/borders/ batting/backing- or are you providing it?
will you be quilting & binding it or sending it out for quilting?
how large of quilts will you be making?
all of these plus probably more-need to be answered in order to figure out any kind of price.
if they are supplying all materials and you will only have time- then you need to estimate how long you think it will take- and how much your time is worth.
if you are supplying materials you need to figure in the price of materials-
i make & sell lots of quilts- generally i start at $350 for a queen and (adjust) from there- depending on circumstances and who it's for- some folks get a (family discount) sometimes i 'throw in' the quilting without charge- sometimes i charge out every penny- if you are supplying materials some people figure that cost & multiply by 3- then add in quilting charge ect. some people charge an hourly rate- but you need to know yourself- and how long it takes you to do things- sometimes- especially if its for a friend or family member- some people just throw out a number- like ' i can do that for about $100 ... then regardless of any issues that may arise that's what they charge-
start with looking at the squares- finding out about who's supplying what- estimate what you think it will take you- and discuss with your friend what seems fair and reasonable to both of you.