Making your own starch is incredibly easy and super inexpensive. I would guess 16 ozs. would be just pennies to make.
Boil 1 cup of water.
Meanwhile . . .Place 1/2 to 1 heaping teaspoon Cornstarch** in a 2 cup Pyrex measuring cup and add a Tablespoon or two of cool water, stir to dissolve Cornstarch.
Add boiling water to dissolved cornstarch, stir thoroughly. Add 1 cup cool water and stir thoroughly.
When cool enough to handle, pour into a spritzer bottle.
Shake well before each spray. This mixture will last 5-7 days then will need to be tossed out (if you even have any left).
**amount of cornstarch you use is a personal choice. The more you add, the stiffer your fabric will be. I personally use 1 rounded teaspoon per 2 cups of water.