db.r6gd.4xlarge is an Amazon Neptune size with 16 vCPUs, 128 GiB memory (AWS Graviton2). In US East (N. Virginia) it costs $4.076 per hour on demand ($2,975.48 per month) for I/O-Optimized storage. It is sold in 8 regions; the cheapest is US West (N. California) at $3.332 per hour.
Prices by region
USD per hour, I/O-Optimized storage. Reserved prices are no upfront, standard. Cheapest on-demand first.