Cost-effective embedding of Tableau dashboards with RDS and Athena as Datasource

I want to use Tableau to build dashboards and embed them into my application. As data sources, I want to use Athena and RDS (Postgres). The RDS instance is located in a private subnet, and from outside of it's own VPC, it is only accessible via a bastion host with an ssh tunnel. One viable solution seems to be to install Tableau server on an EC2 instance, as explained here: https://dkm-website.oss-cn-shenzhen.aliyuncs.com/helpCenter/tableau/tableau_server_linux_aws.pdf . With regards to the minimal requirements, the documents says: "At minimum, a 64-bit Tableau Server requires a 4-core CPU (the equivalent of 8 AWS vCPUs) and 16 GB RAM." The suggested instance types cost between 0.72$ and 1.15$ per hour. If I chose for high availability (i.e. using two EC2 instances in distinct AZs), this would double , and then I have not even covered the costs for Tableau licensing. It seems to me that it might be more cost-effective to use Tableau Cloud, but so far, I was unable to find proper documentation for this setup. In particular, I would like to know if I can connect to the RDS instance in that setup.