Sperm and egg banks just don't accept anyone. There's a standard of donators which they'll only accept. And for some people, that donated egg or sperm means the world to them when they want to have a child. Most regulated clinics only allow for a person to donate a maximum of 10 times to eliminate the probability of genetic siblings hooking up.
I believe it perfectly alright to accept money and be paid to donate sperm or eggs for the purposes of in vitro fertilization or scientific study. Market forces solve the problem of shortages and if people are freely allowed make this decision to enter into the biological asset market then they should be allowed to compensated for their donation.
Being a donor of sperm or eggs is not necessarily immoral. If you are donating out of the perspective that you are giving a family a beautiful gift that they would not be able to receive otherwise, it is a beautiful thing. Some families are unable to have children without medical intervention. For those families, donors are a godsend.
I am not going to cast a judgment on a person who makes a living. The world is a bad place if you can make a living doing something,so be it. The alternative is starving or what ever else. I know I would donate if I had to, blood included.
There is nothing immoral with donating sperm or eggs. Especially if you are in an economic bind and have mouths to feed. Some people need eggs. Some people need sperm. These people make great parents and want children badly, so it only makes sense that these doners are available to them.
I think it is morally okay to make a living off of being a sperm donor or egg donor. I think that while it is an idea that I would not be interested in doing, I do not see anything wrong with it. As long as it's not illegal, it isn't wrong.