think you need to sit down and put together an estimate--what the additional fabric will cost, and then your charge per block (I'm assuming that the blocks are similar and won't need any design work). You need to think about that--are they already squared or will you need to trim, will it be a simple sashing and border added, or will you be doing cornerstones, etc? And will you doing the quilting and binding? I would advise you not work for less than $10/hour minimum. If you can estimate what it will take for you to finish this quilt, great, if not, keep a log-in sheet handy. But do talk to your family member before you start about what will be paid. Only way to be fair to both of you.