RDS is like 4~13x than EC2 on AWS, 2.3x than EC2 on aliyun. https://pigsty.io/blog/cloud/rds/

But The real cost lies on EBS, which is around 60x ~ 200x than local NVMe SSD. https://pigsty.io/blog/cloud/ebs/

https://pigsty.io/blog/cloud/bonus/

RDS can be quite expensive. I wrote a bit on this here https://medium.com/p/6c4fff5a8644