Large tempera cakes fit very well in cheap muffin tins. You can buy the cakes in various sets or individual colors. Tempera can be used like watercolor as well as more opaque techniques. Muffin tins are common in 12 or 6 cup varieties. Use hot glue on the bottom of the cakes. If you want to go super cheap, get the heavy foil tins…But I think investing in some dollar-store actual tins is worthwhile. For classes, I create a set with red, yellow, blue, white and black in a six cup tin for a primary colors set. That leaves you one empty cup. If you want to fill all six, magenta is a great addition. Students can mix a much brighter purple in tempera with magenta instead of red. When dirty, you can rinse the whole set off in the sink under the tap. The twelve color sets shown here I created for gifts.