Can someone please tell me how they have designed eks clusters with different env -prod, staging, dev. We typically provision in two regions, but that would be too expensive. Is there a way to design multi-region cluster for different env

I don't think multi-region EKS is possible and/or supported - Generally multi-region cluster are not recommended, rather deploy 1 cluster per region. I have seen designs with a prod and a single non-prod cluster (with namespace isolation for different envs) or you could use vClusters for each env in a single non-prod cluster.

we do a cluster for each in one region, like Moshe mentioned one way to avoid expense is to have one for prod - and one small cluster with vcluster and within it you can have dev and stage