Blood for oil

Seen at the Heaviest Bike. Related here, here, and here. See also this desperate plea:

I am a college student and am in desperate need of some gas money. If I give plasma the blood bank here they will pay me $50.00. My girlfriend says its stupid but I am litterally running my car on empty and all of my paychecks go to rent money and insurance. Does this hurt to give plasma? How often can I do it? I was thinking if I did it twice a month I could make some extra gas money but would it be healthy?

When I was in college, the stereotype of these plasma centers was that it was all junkies who sold their blood to get their next fix. Seems apropos.