I work at a Fortune 100 and we use fairly well known warehousing database. I can tell you we spend a serious amount of money for our licenses, infrastructure, employee talent, staff-aug contractors and management overhead running this commercial solution. Much of the human resource I would classify as over compensated and non-productive.

We also use some of the previously mentioned visualization technologies and get generally poor results by all measures.

If AirBNB has a few engineers around who are part of solving a unique challenge AirBNB has, then they are probably getting a better deal than we are. I'd wager their productivity per resource is significantly better, not to mention licensing, infrastructure and control over product features. That said, not everyone is AirBNB and has the ability to attract and retain that type of talent.

There's also an in house cost in maintaining vendor software and integrating it. That's on top of the 20% usual maintenance fee.

Building a community can also help distributing the costs. But more importantly it's a labour of collaboration instead of a client/vendor struggle.

> than paying someone to maintaining it yourself

You do realize that this is probably THE reason to open-source a piece of custom software after you've built it, right?

...I imagine that they expect the community will do X% of the maintenance work now, so they can save Y%, so win-win for both the company and the community. Also, you increase the probability that any new hires will be at least mildly familiar with your in-house stack if you open-source some of it (think TensorFlow).

Free as in beer is the best answer when you have reasonable expectations that the community will really embrace the product and you'll get back "free as in beer" upgrades and bugfixes to the software you won't otherwise have the budget to properly maintain (and properly document, btw! think of all the free tutorials that will be written for this after it gets popular!) :)

> Developers have a real, well-documented resistance to paying for things

This is why you never try to target developers and if you do, you have to make sure the initial cost to use it is negligible. This is what Atlassian does very well, with their pricing structure.

In the past, I developed in house tools for massive Enterprise companies and the common theme has always been, we can do it better and cheaper. Sometimes that's true, sometimes it's not. I noticed this trend slowly tapering off before I left to start my startup and this was due to the availability of better open source solutions.

Technical people always overestimate what they are capable of, present company included, and if you are set on selling to developers, you have to make sure the barrier to use is negligible. By at least trying, they will either come to the conclusion that what you have created is a piece of shit or they realize it's not worth their time and effort to duplicate/maintain.