Are you sure that you cannot find spray starch (it comes in a pressurized can) in the laundry section of your market? One major brand is Niagara, and it comes in soft and stiff versions. If you don't like the results, it washes right out.
Cornstarch and water would also wash out easily. I knew people years ago who "starched" doilies with sugar water, but I would be concerned about attracting flies
, or having the sugar dissolve in humid weather.