Like us, most customers use the free version. I believe that licensing for the paid version costs around €20,000 per year.

Oracle Multitenant is suitable mainly for large enterprises due to its high cost and resource demands. There are additional fees beyond standard licensing, which makes it expensive.

I can't speak to the cost. I don't handle licensing. 

Since there is no additional cost for one PDB in a CDB, you should always create a single PDB in a CDB even if you plan on using only only one database. This allows you to practice management of this option and develop expertise in it.

When I was upgrading from version 11 to 12, the budget was limited, so I didn't get the latest version for production.

For me, I will go with it if I have the budget. Some features are nicer than before, but at the end of the day, you always have a limited budget. I prefer to upgrade and get specific hardware when possible. In the end, you will have to make a compromise. You will not get everything you would have liked to have.

Oracle needs to increase the implementation rate and really allow their customers to get some benefit. I would like to allow a maximum of four or five PDBs per CDB for every customer for free (and not limited to Enterprise Edition, but for Standard Edition two as well).

It is worth every penny of investment.