Microsoft Defender Advanced Threat Protection license requirements

PereiraMan  I spent many hours working on this with Microsoft Support.  In the end they tell me that I can only purchase this stand alone license through a partner.  However, they did grant me a trial period which I was able to extend by 90 days.  When I first did the trial is was for 30 days.  It then expired and they sent me an email asking me to purchase it.  I followed the link in the email and there was no way to select that product.  I could only select the "Microsoft 365 E5 Security" product for $12 a month.  Our portal does not show the stand alone Windows Defender ATP for $5.20.  I also asked them about mixing non enterprise products for users.  They said as long as it allowed me to purchase it that it was "legal."  I have some enterprise users and some non who don't require all of those features.  In the end I am just going to have to add the $12 E5 Security to all of my users.  

For some users we have this config:

• Microsoft 365 Business Premium $20 /Mo
• Enterprise Mobile + Security E5
  $14.80
• Microsoft 365 E5 Security $12

But I also see that we could have specified just Microsoft 365 Business Standard
$12.50 / Mo.

What am I missing?