I make my own. It's extremely economical, no preservatives, additives or perfumes, and it's super easy to make with just cornstarch and water, so I always have the ingredients on hand when I need to starch.
Put 1 - 3 tsps. cornstarch in 2 cup pyrex measuring cup.
Add a small amount of room temp water and stir to dissolve cornstarch.
Pour in 1 cup boiling water and stir well.
Add 1 cup room temp water and stir.
Pour into spray bottle.
Shake well before each spray.
This will last about a week. It has no preservatives, so it will go bad after about 7 - 10 days. I never have a problem with that because I usually use the whole bottle before the week is up. If I know I only need a small amount, I half the recipe.
Works wonderfully. The more cornstarch you use, the stiffer your fabric will be, so it's very adjustable to your own preferences. :D