ESRI's product naming can get a bit confusing, and it might help if we straighten out the terminology you are using when requesting licenses.
- ArcGIS Enterprise: Includes on-premise Portal and ArcGIS Server
- ArcGIS Online: Cloud hosted service that is a Portal and the ability to publish and host data layers
There is no product called "ArcGIS Online Portal".
If you are interested in a hosted solution like ArcGIS Online you essentially will need to purchase named users for people to access the system, and credits to cover the different cloud-based functionality (storing data, serving features, performing analysis, etc...). If I was looking to set up an organization with the the items you list I'd be looking at something like this
- 150 viewer licenses: 150 viewer users @ $110 each/yr
- 5 ArcGIS Pro Licenses: 5 GIS Professional Standard Licenses @ $3,025 each/yr
- 10 ArcGIS Editor Licenses: 10 GIS Professional Standard Licenses @ $3,025 each/yr
The GIS Professional Standard License is what's called an AGOL Foundational User Type which means it includes an AGOL Creator named user and 500 credits. So with this configuration you'd end up with 7500 AGOL credits which should more than cover hosting 100 feature layers. If your 100 layers includes raster (aerial imagery or other big raster data) you might need to purchase additional credits for storage.
So all in you'd be looking at something like $60k per year.
Now to compare that to ArcGIS Enterprise (on-premise Portal) and ignoring the additional considerations like purchasing the hardware/VM resources to host everything we are looking at:
- ~$18k for a perpetual Enterprise/Portal Standard license itself (I don't remember the exact number), then $5k/ maintenance
- 5 Enterprise GIS Standard Users @ $7,000/yr, then $2,750/yr maintenance
- 10 Enterprise Editor Licenses @ $800/yr, then $200/yr maintenance
- Enterprise includes "unlimited" viewers to you don't need to purchase licenses for that
So roughly $61k for the first year and ~$20k/yr maintenance... plus physical or virtual machines to support.
These numbers are based on the (limited) pricing I could find on ESRI's site and publicly available pricing schedules like this one (https://purchasing.idaho.gov/wp-content/uploads/ESRI_Price_List_2022.pdf). Pricing increased a bit for 2023 so nothing should be taken as gospel.