Jay wants to know if there's a Kelly Blue Book for computers? Leo says no. Computer values disappear rapidly because there's no real resale market. There are so many different PCs, that it would be a very large book if there were one.
One way to determine what a computer is worth is to search eBay's listings. That's a good way to see how much people are paying for it. Jay shouldn't buy a used computer, though. It's a false economy to get a used one. He's just buying someone else's problems. If he wants to save some money, he should get a factory direct refurbished computer.