As a recipient of blood products myself for when I had cancer I think your being pretty rediculous. A coupon system would be rediculous to track plus keep in mind that the hospital administering the blood incurs most of the liability, if you get sick as a result of tainted blood your going to sue the hospital, not the red cross. So even if the cost of the blood itself is free the hospital is still going to load on the costs.
But more to the point, it would be very risky and dangerous to pay for blood. The list of reasons for permanent deferral for donation of blood is rather long. Chemotherapy for cancer, for example, is one reason. As long a blood donation is voluntary, people like me who are on the permanent exclusion list have no incentive to lie to the red cross in order to donate. If you start paying for donated blood then all the druggies and addicts looking for their next fix would be running into the red cross and selling their blood, and of course would lie about being druggies in order to not get deferred. We don't need blood from people like that in the blood system. Besides wasting a lot of money when they test it and have to dump it when they find drugs in it, I don't even think it's possible to test for every single pathogen that might be in someone's like this blood.
Ted