Pricing of Key Pairs and Security Groups on AWS?

There should be no charge for either of those things.

It's a bit of a stretch to call them "resources." In the world of AWS, and in contrast to the other items on that list, those items are more like "metadata." (The same logic applies to Placement Groups.) You'll potentially need them if you launch future instances, but they aren't consuming anything resource-wise at AWS except for a tiny amount of storage, which isn't billable to my knowledge but I am unable to cite any authoritative documentation saying so.

You can See in your AWS Billing Dashboard There no Additional cost of securities group.