Hello @CJ Shields Thank you for contacting us!
In your post you have mentioned that, you see two subscriptions, pay-as-you-go subscription and Standard support subscription. Also able to see invoice for both. However, unable to assign permissions to anyone to view standard support subscription.
AFAIK, there is no such subscription called "Standard support subscription". It is a support plan not a separate subscription. Reference link - https://azure.microsoft.com/en-us/support/plans/#:~:text=Compare%20support%20plans%20%20%20%20Not%20available,%20%20Available%20%2011%20more%20rows%20
Also check the different types of Azure subscriptions that is offered by Microsoft Azure - https://azure.microsoft.com/en-in/support/legal/offer-details/
As far your question to assign other users access to view cost management data, you must have owner or user access administrator permissions. See the article - https://learn.microsoft.com/en-us/azure/role-based-access-control/role-assignments-portal?tabs=current#prerequisites
Check this URL - Assign access to Cost Management data
Hope this helps!
----------------------------------------------------------------------------------------------------------------------
If the response helped, do "Accept Answer" and up-vote it