I think you should factor in woodgrain vs not in your formula.
Then here is a universal buying vs selling stratagy.
Lets say we want to buy an item, we'd like to spend $10. for it. Now the same item to sell, use the 10X factor and it is now at $100.

It's only worth what it is worth to you (or a buyer) we've all seen inexpensive items go for crazy high prices and visa versa...
Hypothetically speaking of course...