1. Buy a metal clamp at a hardware store. Make it about a slingshot size, or however big you want it. My clamp cost $1.29
2. Cut a pouch of leather, cloth, or any fabric you can use lying around the house into a pouch. Then hole-punch two holes into it, and tie rubberbands to those
3. Tape or glue the rubberbands and pouch onto the clamp!! Yay! Now it's allready and you can have fun!
Not as good as slingshots for sale, but good for safe fun!