Vintage pen pricing: or, "Why does this one cost so much more than that one?"
We are often asked why two apparently very similar items can have such different prices. The short answer is "supply and demand". The longer answer is that collectors seek out the unusual, and will pay substantially more for pens and pencils in uncommon sizes, colors, and trim configurations. A mustard-colored Parker 51, for example will cost a few hundred dollars more than a black one, even though the two pens are identical aside from color. And in many cases, the rarer color is the more delicate material, as with yellow Duofolds. By and large, the more expensive version of a given model will not write any better than the more economical. The main exception is with unusual nibs -- very flexible, italic, oblique, etc -- which will raise the value of a pen, though usually not nearly as much as some other rare feature.
Condition is another important factor. Older pens in top condition are much, much scarcer than ordinary used specimens, and unused pens with original price stickers are rarer yet. If you are buying a pen to use, it makes no sense to pay the substantial premium for a mint example when another that is only lightly used goes for so much less. At the same time, don't settle for a heavily worn pen unless it is quite rare or you are buying it strictly for function, and be careful about comparison shopping between sellers without making due allowance for differing grading standards. Too many sellers take a "don't ask, don't tell" policy when it comes to disclosing flaws, while others describe anything not obviously broken as "excellent".