Very simple to make and very, very cheap! Perfect for bathrooms or closets. Will last around a month.
The instructions for this will depend on the type of gelatin or pectin you use.
What you'll need:
plain, unflavored gelatin or pectin
water for preparing gelatin
food coloring (optional, just for added flair)
small glass jars or bowls (I filled three with 2 cups of finished gelatin)
1 tablespoon salt (prevents mold)
To make this, place 1-2 drops of food coloring in each of your glass jars or bowls, and then prepare the gelatin according to the package directions, adding the salt during boiling. Once the gelatin has dissolved in the water and it's ready to set, add 20-30 drops of essential oil and mix. Then pour into your individual containers and mix with the food coloring.
Check the strength of the smell at this time and add more oil if necessary.
This will firm up at room temperature, but if you want it to set quicker you can place it in the fridge.
I've got two of these in my closet right now, as well as one in the bathroom.
You can cover these with thin cloth or perforated paper if you like, but I keep mine up high enough that anything that sticks to the surface is out of sight. :)