VPC endpoints are great, but they come with some quirks and cost is one of them. While using them, one should be aware of their finops.
In order to use the VPC endpoints, remember that there are two kinds of endpoints. One is Gateway and the other one is interface. Gateway type is free which is great but unfortunately that is only available for S3 and DynamoDB. For rest of services, you would need to use interface which is not free. Roughly the cost is as follows:
$0.01 per hour per endpoint per AZ (~$7.50 per month) plus a $0.01 fee per GB of data processed. If you have three AZs in your VPC, you’re looking at a base cost of $22 per month in addition to the data processing charges.
So beware of the cost before you opt for one.