I agree that you should be paid at least $10/hour for skilled services and wear & tear on your machine. Having said that, let's estimate that to prepare & cut your yardage, press, square and sash each block takes 15 minutes. That's $150 right there. Then there's sandwiching, quilting and binding. Probably another 10-15 hours, or $100-$150, so you are looking at at least $250-$300. I would tell them that you will charge them by the hour, but your rough estimate is $300, plus materials (which I would have them purchase). Purchasing the materials is often an eye opener for non-quilters.
Even if it is a very close family member, have this discussion before you start, and put it in writing!!!!