Looking at the GKE price calc - N2 machines (which i have no idea if they are cheapest per vcpu/mem) * 7 will give you 896 vcpu and 3584 GB ram. that will cost you 21K per month for a zonal cluster
we can do napkin calculations but that won't help you. if you want to get your bill down you just need to open the billing reports and start slicing data by usage
Edit - i really hope i am not coming off as condescending or anything. I used to work in a startup related to cloud cost optimization and currently as a devops in a cloud env so i know how these costs can get out of hand.