And, for better or worse, what you're left with for coming up with base cost is whatever you think it's worth. Information is nebulous like that, to one person, knowing where I plan to build my fence might be seen as invaluable, and they'll pay 200¥ for it. To just about everyone, it's worthless.
Even FastJack's example of Damien Knight's personal calendar / little black book. To many (most) in the megacorp world and shadows, it's worth a large pile of diamonds. To Damien, it's probably worth twice that (if you can get away with selling it back to him).To at least a few people, it's worth nothing.
So, if it's generic "paydata" that you never gave a description of, decide how much ¥ you're willing to hand to your players, or figure out a random system you like (roll a DP equal to the net hits your hacker obtained to get on the node, multiply the result by 500¥, instant pay-data value). If you did give him an idea what it was (the formula for New-SoyCaf), decide what it's worth to the people the hacker's fence knows (or the person the hacker is selling it directly to) and offer that up. Same process as deciding what a Johnson would pay a runner team for the intel.