This completely ignores customers without boatloads of cash laying around. I've worked in educational institutions where there is absolutely no budget to do something. However, people that are genuinely interested in accomplishing something will turn to open source.
They have time to contribute back through documentation, bug reports, and even bug fixes. The only thing they don't have is money. That doesn't mean they don't value the project.
If you're interested in seeing something open sourced and you have time but not money, consider offering to do some of the requisite cleanup work under NDA.
"If someone won't pay for a closed product, and won't pay to open it up, they don't value it at all."
There might be no/little value in the product but some probability of value in the source. For example, for a competitor there is possibly a lot of value in seeing the approaches the software took, the problems the developers ran into, etc. Key word: Possibly.
I'd personally just ask to interview the startup owner for 10 hours at say $200/hr but I know some people aren't great at extracting value from a face to face chat.
Value is not an objective property of a thing, so I don't see your point. Things have value by the virtue of them being valued, not solely because someone wants to spend money on it.
Actually there's an entire spectrum of pricing between paying enough to get the owner to agree to give the product or the source to you, and wanting it for free.
Price determination is always hard in business, but I'd like to think its a bit easier with software or SaaS products, as you have zero marginal cost (besides server time).
They have time to contribute back through documentation, bug reports, and even bug fixes. The only thing they don't have is money. That doesn't mean they don't value the project.