We already have a sperm/egg donation industry. Why not pay people to be blood donors? I'd probably participate, although the only blood I've donated so far was just a couple of small vials for a study. Aging members of society would get younger blood, which young people such as myself already have plenty of. I get money, which (if I'm still in college by the time people want blood transfusions) they have a greater capacity to earn than I do. Everyone seems to win.