Underwood Typewriter

From what I can garter the value is subjective when it comes to typewriters. It seems that $50 is concidered a top end price and that is if you can find a buyer willing to pay that.
This is a link u may find informative
http://www.typewritercollector.com/classifieds.html

an excerpt from the link:
On Prices:
Prices for typewriters depend on many things, including (above all) rarity of the model, uniqueness of the mechanical design, condition of the machine, and personal predilections. Prices can vary a lot. Some years ago Paul Lippman wrote, "The value of a collectible typewriter is very subjective, differs from one part of the world to another, and changes constantly. No two collectors would agree on a specific value anyway. It still comes down to what a buyer is willing to pay and a seller is willing to accept."-- Paul Lippman, American Typewriters: A Collector's Encyclopedia. If you want to build a collection, I recommend buying the recent books by Darryl Rehr and Michael Adler. Both include suggested values; they differ widely, and you should consider them to represent the upper (Adler) and lower (Rehr) extremes of the normal price range. For a discussion of the approximate value of some common makes of typewriters, see. Prices for most typewriters advertised on this site are normally negotiable, and do not include shipping.
On Condition:
The condition of a typewriter can affect its value significantly. You may want to use the following terms when describing the general condition of your machine, or at least keep the following features in mind.

* Excellent = glossy paint, shiny nickel, no rust, no missing parts, types well.
* Good = gently worn: minor nicks and scratches, minor flaws in nickel, no missing parts, minimal rust, capable or nearly capable of typing.
* Fair = significant damage to appearance and/or mechanism, but restorable. Rust damage, missing paint or decals, mechanical problems.
* Parts = not restorable; useful only for parts. A rust bucket.

How does one conduct a search of typewriter serial numbers? I, too, have an old Underwood and would like to know more about it.