There's no ArcGIS Developer Subscription which allows a developer to get low-cost access to ArcGIS Enterprise Basic or Standard. For those who do not work for generous organizations that have the funds to pay $1,800 year for the Professional subscription, or for those who just want to get started with ArcGIS Enterprise on their own, the $1,800/year cost for Professional is pretty steep.
Please consider creating add-on ArcGIS Enterprise license packs for the Essentials and Builder subscriptions at a cost of say $150 and $300/year respectively.
