Apple Business Manager is free. Apple Business Essentials is and MDM (like Intune) that requires a subscription. You DO NOT NEED Apple Business Essentials to accomplish what you want to do.
A couple of suggestions and an expansion of explanation.
ABM is for chain of custody of hard (Macs, iPhones, iPads, etc.) and soft (software licensed or purchased through the App Store as well as books) assets. ABM can also participate with your identity provider through Federation and Sync. For Managed Apple IDs (MAIDs), you should consider Federation and Sync to avoid manual creation of the IDs and the creation of yet another password. Note, if you have been around a while, you will likely need to reclaim IDs that use your domain. This can be a process.
Next, you should be striving to automated device enrollment. I get it, you are using Intune and you have no User-Initiated enrollment option. So you are stuck with Account-Driven or you are likely stuck wiping and side loading your existing hardware. While Account-Driven is your "I want to get everything managed fast" path, it should not be your end goal. Make sure you are connecting ABM with your hardware reseller (or Apple if buying direct). By purchasing properly from the start, you hardware will simply appear in ABM and you can setup automatic assignment to your MDM (Intune).
Bottom line, if you are planning to use Intune as the MDM, only sign up for ABM. There is no fee for this.
Hope this helps
