Epoxy Cpes, raka, west,fgci

Hello all, I am building a 4x8 tear and not wanting to spend more than needed. Does anybody know about how much it will cost covering 2 coats of epoxy and is there a product less expensive than another?
I hear some using exterior primer and paint with no epoxy is that a mistake
I am not building the Taj mahal but don't wanna short change myself
Thanks
I hear some using exterior primer and paint with no epoxy is that a mistake
I am not building the Taj mahal but don't wanna short change myself
Thanks
