To date; effective anti fouling
means using heavy metals in the paint
(especially in high-fouling regions). It used to be tributyl tin (now banned throughout most of the world) but is now primarily cuprous oxide. As you are discovering, these metals are not cheap
. There is no inexpensive alternative that works well. Just bite the bullet and use a good anti fouling
product from a reputable company. You will likely regret your decision otherwise.