Mongo is quite unrepresentative here - not least, because they're selling the very same software (MongoDB) under both OSS and proprietary licensing! A better comparison in the database space would be e.g. PostgresSQL - the latest versions of which, BTW, are including "NoSQL"-focused features that make it quite competitive with the likes of MongoDB.
https://www.linux.com/publications/estimating-total-cost-lin... (mind you, that's 2008 data. I couldn't find more recent estimates)
Mongo is quite unrepresentative here - not least, because they're selling the very same software (MongoDB) under both OSS and proprietary licensing! A better comparison in the database space would be e.g. PostgresSQL - the latest versions of which, BTW, are including "NoSQL"-focused features that make it quite competitive with the likes of MongoDB.