Each female cat can have three litters a year. Most litters are between four and six kittens. Depending on how many females are in the litter, at about the age of four months, each female kitten can start its own cycle, etc. You do the multiplying. Don't delay, especially with cats.
Time is of the essence.
If you don't have the money for the clinic, call your local shelters and they can probably refer you to someone who can help you. For those of you who have the males, you can help, too. Even though your male is not giving birth, he can father many litters. Get him neutered. For those of you who do not have pets, while you're angry at those who do not spay or neuter their pets, and while you feel it's not your responsibility, you can help by donating funds to organizations who, in turn, will help others.