Here is a great recipe for homemade playdough. It's cheap, non-toxic, and kid-approved (my kids love it)!
1 Cup of plain flour
1/2 Cup of salt
1 Cup water
3 dessert spoons of cooking oil
2 teaspoons of cream of tartar
Food coloring (optional)
Mix all the ingredients together. Mix until all the lumps are blended. Put mixture in a saucepan and cook it very slowly over medium heat. Stir continuously. When the dough starts to come away from the sides of the pan, remove it from heat.
You could also add scents to the playdough if you prefer.
This is by far one of the best playdough recipes I have ever used.