The base use cases are "I want my users to be able to login in MS 365 from company managed devices". and "I want to manage my company's devices".
OP was probably thinking of Microsoft 365 E3 which does cost $36/user/month. That however includes a bunch of other stuff besides Azure AD P1.
It’s hard to buy Azure AD alone, they push the EMS suite and O365 E5 to solve the security issues in O365 E3.