Maybe it's the accountant in me (and I have not knitted for others - too new) but on July 24, 2008 the minimum wage (MW) will be $6.55 per hour here in the US. How many hours will it take you to knit the afghans? Are you at least worth MW? Is this a friend or a prject you want to do and wouldn't if it were not for someelse, maybe I would go below MW.
You are worth a reasonable "wage" even if it is only that they will keep you supplied with coffee and donuts until you are finished.