Make the onlibne value guide a chipipedia. Let the users update values themselves.

Example: a chip starts with a value of $25. Person "A" adds: "Paid $22 from fellow collector". A day later, Person "B" adds: "paid $24.95 on ebay". And so on. A history for the chip develops over time. Maybe person "C" adds: "trade for chip XXX". Such a history would be the best possible information. And its done by users just like wikipedia