[sheepmullet]

"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.