The t206.org value estimater is a valid concept as a way to think about values. It has unfortunately not been maintained and updated to be currently accurate, but the idea of a common base value times a back multiplier times a condition multiplier is a good way to approach values. Trae Regan put together the original concept, I believe, and Scott Reader has done updates on the back multiplier end of it. All three components can change with time for any given card.
I would add a museum pricing estimater as well. This is quite easy and can be accomplished by simply adding a zero left of the decimal point of a market value price. Using this tool on EBay will assure maximum exposure for your card as it will sit there forever and never be sold.
