To tag onto the idea Darren Wiens posted, you may want to explore the advantages/disadvantages of having an enterprise license. Having this information formulated will help buttress your choice - it is not uncommon for decisions on funding to be questioned. What does your organization use if for, and what are the alternatives? Does it serve your organizations needs? Is it sufficient or insufficient for what is currently needed and what is planned in near future? For example, what if the organization changed to just ArcGIS Desktop licenses - would that impact things? For better or worse?
Also, licenses vary, so you may want to provide some specifics on what your enterprise license currently includes. This will help the GeoNet folks you are appealing to in providing good examples that match your situation.
ArcGIS Platform | Pricing
If it is determined that an ESRI enterprise license indeed is very valuable, you may additionally want to talk with ESRI for suggestions on helping to explain the value. They may have already developed resources that you may be able to tap into.
Chris Donohue, GISP