Hi @Mike Gallamore ,
There are a few options to set up free Azure services. The resources and services you use will determine whether you need an Microsoft 365 license, a Premium P1 License, or a Premium P2 license. There is a good comparison chart in this article: https://learn.microsoft.com/en-us/azure/active-directory/fundamentals/active-directory-whatis
To get 12 months of free services and $200 of Azure credits for 30 days, you can follow this link.
To get a free trial of Azure AD Premium, see this link.
The Microsoft 365 bundles also come with different Azure AD licenses, and that's where you would have seen the Standard and Enterprise options you mentioned. https://learn.microsoft.com/en-us/office365/servicedescriptions/microsoft-365-service-descriptions/microsoft-365-business-service-description
With the free version, your users will be able to sign on across Azure services, but a lot of the hybrid features will require a Premium license. I would recommend speaking with a billing representative to get free guidance for your particular scenario.
For authenticating third party identities, you would want to leverage Azure AD B2C. B2C has a free tier for your first 50,000 active users per month (MAU) and has incremental pricing for Premium P1 and Premium P2 features.
Let me know if this helps.
https://learn.microsoft.com/en-us/azure/cost-management-billing/manage/avoid-charges-free-account
https://azure.microsoft.com/en-us/free/free-account-faq/