Hi and welcome.

I hear you on the price of almond flour. Not only is the coconut flour less expensive pound-for-pound, but most recipes with coconut flour call for a lot less of it.

They don't really substitute for each other. Coconut flour is very dry, and absorbs a lot of moisture. You might want to google around for a tried-and-true recipe.

If I was going to play with the recipe, I would probably add more egg and some oil and/or water. I also tend to add spices with coconut flour to help cut the "dessert-like" quality it has (at least to me.)

Have you considered flax seed crackers? Flax is cheap here in Canada; probably because we grow a lot of it. You can bake them, but I have a dehydrator and prefer them that way. I usually add coconut flour to those, too.