I think I found the spreadsheet everyone was discussing online....
http://www.t206.org/resources.php
After you reach this page, look at the bottom left (last link), called "Bill Brown's Super Set Spreadsheet".
Also, there is another spreadsheet called "T206 Excel Database by Mike Poland" that appears to calculate values and help keep inventory.
On the mail menu, there is also a Valuation page that lets you look up prices on the fly, not sure how accurate it is, but one of the easier tools I have found to use.