Spayed and Neuter My Fur Babies

I Have 20 Cats Both Male and Female I Can Afford To Love and Feed, But I Can't Afford To Get Them All Fixed To Prevent More Litters
 Males Cost About $50 and Females Cost About $165 which On A Fixed Income Just Can't Be Done
 I Have 7 Males and 13 Females
 I Love Them All But Can't Afford Any More
 Please Help Me Control My Pet Population

We All Appreciate And Thank You For Any Help