Collecting Antique Typewriters
The monetary value of a typewriter can't be determined precisely, because there are relatively few collectors and the market is always changing. Furthermore, the condition of a typewriter affects its value significantly. To further complicate things, there are literally hundreds of makes of typewriter that are of value to a collector, ranging from $50 machines to $50,000 machines. However, you should first check to see whether your typewriter falls into one of the classes below, as 95% of them do.
Postwar typewriters
Very few typewriters made after World War II are considered "collectible," because these later writing machines are mostly look-alikes produced in great quantities -- and are often pretty ugly. Someone may want them, of course, but don't expect the price to go over $20 or so. The exceptions to this rule are typewriters that have a strange or specialized mechanism -- for instance, the Varityper, a "cold typesetting" machine descended from the Hammond which prints from a type shuttle.
As for prewar typewriters, most belong to the following makes:
Corona
This is one of the first portables. The Corona that most collectors like has a carriage that folds down onto the keyboard. This is a beginner's machine that is frequently found. An informed collector will hold out for one in excellent condition, and will not pay much more than $50 for it. Colored specimens are worth more than black ones.
Oliver
These machines are collectible and are certainly unusual to the modern eye, with their U-shaped typebars hovering over the platen. However, most are not rare. Expect the value to be in the $50-$100 range, give or take some according to condition. Olivers do have many minor variations, some of which are unusual. The most valuable Oliver is the #1, which can be recognized by its nickel finish and the fact that the tabs sticking out of its sides are flat to the ground.
Remington
Remington was always a leader in the typewriter industry -- so many Remington machines are common and worth little. Understroke Remingtons (which type on the underside of the platen) are worth some money; these are full-sized, office typewriters with model numbers under 10. The most common understroke Remingtons are the #6 and #7, worth around $100; other understroke models can be worth more. There are also many models of Remington Portables; most of these are frequently found, but are enjoyed by some collectors. They will bring a modest price, say $30. The Remington Electric of 1925 is worth several hundred dollars; this is a very boxy machine that has a carriage return lever on the right.
Royal
The Royals to look for are the #1, #5, and Standard. These are office machines with an unusual, low profile and a keyboard that looks like it's emerging from a staircase (collectors call these the "flatbed" models). They are worth around $50-$200 depending on condition (usually they are in poor shape). Many older Royal office typewriters are model 10 (usually not marked as such); the earlier ones have glass windows on the sides (pretty although useless). Value depends on condition -- anywhere from zero to $100. The Royal portables are fun, but not worth much (about $30). Finally, if your machine says "Royal Grand," you have found a very rare item that's the most valuable model of this make.
L.C. Smith
These are common, conventional typewriters. The earlier L.C. Smiths have a handsome decal with prancing horses. If you have such a machine in excellent condition, the lower the model number the better, it can bring $100 on a good day. L.C. Smith merged with Corona to create Smith-Corona in 1926. Smith-Corona portables from the 30s, in excellent condition, can be nice and might be worth $50 or so. Later Smith-Coronas are of minimal interest to collectors (although they are fine writing machines).
Olympia
A very successful German make, with a reputation for high quality. Because supply far exceeds demand today, it is unlikely that an Olympia will bring more than $50.
Underwood
The Underwood was the IBM PC of its day -- popular, reliable, common, much-imitated, and frankly, pretty dull. The earliest Underwoods are considered collectible and will bring roughly $200; these usually say "Wagner Typewriter Co." on the back. Some collectors or people who want one old typewriter will enjoy an ordinary Underwood (which is likely to be a #5) if it's in great condition. Very nice #5's can bring $150, but the average-condition Underwood (any model) is difficult to sell at any price. There are some nice Underwood portables, particularly the "Underwood Standard Portable Typewriter" of 1919-29, with three rows of keys (the name is bigger than the typewriter). It's worth about $40.
Woodstock
These well-made but conventional typewriters are generally ignored by collectors. The Woodstock Electrite is an early electric typewriter that is not frequently found, but still may bring under $100.