I really want to go to azure - and I know it can be cheap to start - but the pricing calculator seems to be a black art.
I'm curious what real world looks like? 50 users?
Heavy API usage?
For web app hosting on Azure, Linux OS web app can be used best , since it is very cost effective.
Please refer below link for the details -
For database pricing, use the following link - [https://azure.microsoft.com/en-us/pricing/details/sql-database/single/] You can use these parameters to get more idea on the database pricing
Purchase Model - DTU, Service Tier - All, Display pricing by - Monthly
Additionally, if this is a multi-tenant application, it requires custom domain and wildcard SSL certificate as well. The annual pricing for Wildcard Certificate is 299.99 USD approx.
For your case , assuming 50 users and heavy API , B3 web app plan would be optimal. (For single solution aspnetzero)