db.r6gd.large is an AWS RDS size with 2 vCPUs, 16 GiB memory (AWS Graviton2). In US East (N. Virginia) it costs $0.257 per hour on demand ($187.61 per month) for PostgreSQL, Single-AZ; a 1-year reserved instance with no upfront costs $0.198 per hour, 23% less. It is sold in 23 regions.
Prices by region
USD per hour, PostgreSQL, Single-AZ. Reserved prices are no upfront, standard. Cheapest on-demand first.