I copied and pasted several recipes for homemade spray starch from other posts on this board. The (optional) lavender oil is just for fragrance, so it's very inexpensive (probably have cornstarch in you kitchen cupboard).
Homemade spray starch recipe
This is a great money saver and it does an excellent job.
Dissolve 1 teaspoon to 1 tablespoon cornstarch (depending on amount of stiffness you want) in a few tablespoons of cold water in a heat proof 2-cup measuring container. Add boiling water to make one cup, stirring constantly. Then add cold water to the 2 cup line. Let cool and use in a spray bottle.
Shake it every time you spray.
You may have to dilute it a little if it is too thick or builds up white flakes.
Discard after a week or so and make a new batch. You can also refrigerate between using to keep it fresher.
I heard of people making homemade spray starch and adding a small amount of clear vodka to help it last longer, i thnk about 2 oz of vodka to a recipe similar to this site:
http://tipnut.com/homemade-lavender-starch-recipe/
Lavender Linen Starch
Dissolve 1 tablespoon cornstarch in 1 pint cold water. Add 6 drops of lavender essential oil. Place in a spray bottle. Shake before using.
Fresh pressed linens, nicely starched, and lavender fragrance wafting in the air. Nice!