It is illegal to sell blood, but it is legal to sell blood products like plasma. Depending on the area of the country and your health status, plasma donations pay $15 to $40 per donation.
Yes, the first time donation maybe higher than the other times. It is not a lot of money it is usually between forty and seventy five dollars a week. The last time it was last like sixty dollars and that was going twice a week for the donation. It usually is every two to three days you can go.
If you have a disease like Hepatitis, Lupus, or another, you can donate plasma and make $400+ per donation for research studies. Google companies like SeraCare Life Sciences or Biospecialty Corp to find these studies.