You’ll need a license for Visual Studio to do the development (express editions are fine if you can get away with them).
For production use you’ll need a SQL Server license. If the application is Internet facing you’ll need to use the CPU licensing model. If the application is internal only (only employees using it) then depending on your enterprise licensing model you can use either CPU licenses or CAL based licenses.
For the web servers you’ll need Windows licenses. If the app is internet facing you’ll also need to purchase an Internet connection license. It’s a couple thousand bucks and will cover all the servers you have. If the app is internal only then as long as all your users have Windows CALs (which they are required to have) then you are fine.
You’ll also need a Windows license for the SQL Server. Nothing special there, just the Windows license.