One of the most favorite activities of some of the kids in our playgroup is to pour, dump, scoop, and sift through rice. I filled up Safi's water table with some colored rice this winter when we had it set up in the garage and since the weather has warmed up I moved it out to the backyard (so much easier to clean up now!).
I got a bigger table and it called for some new rice, after about six months the rice that was left wasn't as colorful any more. So I got a 50 lb. bag from Costco (about $15) and began the process of dying the rice which didn't take long at all. I didn't measure anything I was just dumping but I used less than a bottle of alcohol for the entire bag of rice, but I am sure that I used more food coloring so the colors came out really vibrant. This can also be done with pasta and works just as easily and is great fun also.