At the risk of being trite, you've hit the nail on the head: there's no real set price. It depends on the data source, quality, recency, collection methods, how

At the risk of being trite, you've hit the nail on the head: there's no real set price. It depends on the data source, quality, recency, collection methods, how tightly focused it is, and who the customer is. I'd suggest doing some background research on the company in question; if they're talking to you, they'll have talked to other people, probably in your area, probably in others before too. See if you can find some of their names, and see what they did. Also, start digging around your area in general, and see if anyone else is selling data. If so, find out what they're selling, how they're packaging it, and what they're charging. Step one of selling anything is understanding the market. Know your competitors. As a second step, once you know what the going rate is, package your pricing around that. You should be able to work out based on other people's pricing methods what your data is worth to this particular company. Bare in mind though that what it's worth to them might not be what it's worth to other people in the future, so have some flexibility built in there too. Finally, in data sale, as with everything, there's room for negotiation. Ask yourself what you'd consider a fair price, combine that with your other data, and work from that. However, I'd also raise the question of, is this something you want to do, and how would your customers react if they knew what you were doing? There may be moral, ethical and legal issues to answer, although not knowing the specifics, I can't really comment there. Hope this helps!