The economics of sperm donation.

A man can only donate sperm about once a week and must abstain from sex otherwise to maintain the concentration necessary. Typical payment for a closed (anonymous) donation can be as little as $20 to $50. Open donations, where the prospective parents get to meet and interview the donor can pay more but are time consuming to set up. To make the amount of money (over $20000) claimed in the movie in would take decades. A single donation can be used to impregnate up to 20 women, however this is very unlikely since the failure rate for artificial insemination is close to 90%. The number of children claimed in the movie (533) would be close to impossible. In a few cases men have fathered hundreds of children but this has typically taken decades of donations. Many donors are medical school students.
It is also possible to a arrange a so call natural insemination. This is exactly what is sounds like. This is sometimes the preferred method for single women who wish to become pregnant. Doing so through a sperm bank assure the women that the man has no diseases or genetic problems. Usually multiple "treatments" are required. Eventually the women gets pregnant, the man get paid and he get to brag about it FOR THE REST OF HIS LIFE.