The 50 lb. bag of sand I used was $3.69. And then I used about 6 cups of corn starch, and a tablespoon of dish soap. Plus water I started with about 6 cups, since you need 50/50 mix of water and cornstarch to make Ooblek, and kept adding until it was the right consistency. What you Need to Make 50 lbs. of Kinetic Sand: 50 lb. bag of sand: $3.69