I've decided to try out a recipe that I found on Pinterest for home made chalk. It was really easy and didn't take very long to whip up. The waiting part took overnight but I can deal with that. You need: plaster of paris, water, food coloring, rubber scraper, a glass mixing bowl and mold of your choice. We used soap making molds.
Mix the plaster of paris 2:1. I started with a cup of plaster and 1/2 cup of cold water. That gave us enough to fill two big squares on our mold tray. After your plaster is mixed, you can add 8 drops of food coloring if you want. We tried adding 8 more to see if the color would be darker but it didn't seem to change very much at all.
Mix well and pour into your mold tray. Gently tap the bottom of the mold against the table to release air bubbles.
Rinse your bowl immediately after your done with hot water and make more using different colors. Let them sit overnight to dry out. Carefully pop them out of the mold and VOILA!! We found all of our supplies at our favorite craft store AC Moore. If you sign up for their emails, you get a 40% off coupon each week. Thats when we bought our plaster. I think the coupon brought it down to around $5. That 4.4 lb carton will last us through several batches. So chalk IS cheap.