AWS Managed Rule Pricing

I completely read the AWS page for AWS WAF pricing, however I am still not sure how much would it cost if I create a single AWS WAF and hire just the AWS Managed Rule Set "Core Rule Set"

As I understand it should be 5 US/month for the WAF and just 1 US/mont for the complete Managed Rule Set because its rules have not been created by me and each Managed Rule Set costs 1 US/month, and that should be that

There is the possibility that the "Core Rule Set" would cost 23 US/month as it has 22 rules, and I am not completely sure that I will not be charged by them as I do not find it to be explicit enough from the Pricing page

So would it cost 6 US/month or 28 US/month? I find it quite a big difference bucko

You are correct with your first line of thinking. Each WAF is billed at $5 USD per month and each rule that you create is billed at $1 USD per month.

You will be charged for each web ACL that you create and each rule that you create per web ACL

You will be charged for rules inside rule groups that are created by you. In addition, you will be charged $1.00 per month (prorated hourly) for each rule group or each managed rule group that you add to your web ACL.

Note that rule groups that you get from the marketplace can be charged at any usage rate that the seller desires, but the flat pricing is always the same.

When you subscribe to a managed rule group provided by an AWS Marketplace seller, you will be charged additional fees based on the price set by the seller. These charges are in addition to the AWS WAF fees described above.

Basically the distinction here is rules created by you vs rules created by a seller or AWS. Rules that you create are always charged at $1 USD per month. Rules created by sellers or AWS are never charged to you directly

For your situation, you're looking at the Core Rule Set, which is a free managed rule group provided by AWS. You will be charged $1 USD per month for adding a rule set, but there are no additional usage charges for the free rule sets. This is in contrast to something like the Bot Control rule group, which is not free in that it charges based on usage on top of the $1 USD per month for any rule group.

I plugged these into the calculator at the bottom of the pricing page and got these results.

1 Web ACLs per month x 5.00 USD = 5.00 USD (WAF Web ACLs cost)
1.00 Billable Rules per month x 1.00 USD = 1.00 USD (WAF Rules cost)
5.00 USD + 1.00 USD = 6.00 USD
AWS WAF cost (monthly): 6.00 USD

https://aws.amazon.com/waf/pricing