Wal-Mart also ha a $4 prescription list. Seroquel might be on it. I'm not really sure. It's worth looking into though.
The label on the script should tell you who the manufacturer is. You can contact the company directly, contact your local health dept to see if they have a program to help with the cost, or look into charities, like the Montel one, that give away meds for free if you qualify. Most states now have programs for free mental health care and meds if you can't afford them yourself.