This are surprisingly easy to make.  It is one part powdered citric acid to two parts bicarbonate soda.  As mine are only mini bath bombs, I used 1 tablespoon to 1/2 a tablespoon, but it works just as well with 2 cups to 1 cup.
Mix the citric acid and the bicarbonate and add a few drops of food colouring if desired and a few drops of essential oil to make it smell nice.
Add, drop by drop, sunflower oil while mixing.  Keep mixing until the mixture starts to stick to the sides of the bowl.
Tip the mixture into cling film and using the cling film as a barrier, so not to touch the mixture, shape the mixture into a ball.  Leave to dry over night.  If you've added too much oil it may be a bit sticky in the morning, but it works just as good.  Store in a dry place.

This is probably one of the most easiest and cheapest things to make if you already have everything in your kitchen cupboard.

You need:

• 2 cups of brown sugar
• 2 teaspoons of vanilla essence
• 2/3 of a cup of olive oil

All you do is mix them all together in a bowl and boom you're done.

If you are going to store this, I suggest stirring it before use as the oil does have a tendency to separate.  Also, if it doesn't smell enough of vanilla for you just ad a splash more vanilla essence.  I would also suggest to not use this around the face as the sugar can make it quite rough.

To use just rub into your skin and then wash off with warm water.  Please don't use it if you are allergic to any of the products.