The Value of Common Typewriters
Since there were so many typewriters produced and sold over a time span of 100 years or so, the first step in determining the value of an old typewriter is figuring out whether it is a common model. Searching on eBay.com and online antique shops can give you a good idea. You can also visit brick and mortar antique malls and shops in your area selling vintage typewriters. If you see the typewriter you own listed or displayed for sale over and over again, it's probably not going to be worth much to a collector -- generally less than $200, and in some cases much less.
Common Manufacturers: Remington and Underwood
Two common manufacturers are Remington and Underwood. Collectors don't view all the models these companies made as commonly found examples, but it's wise to keep in mind that they were prolific distributors and the likelihood that you have an uncommon model is low. For example, Underwood sold millions of its No. 5 model over a 30-year production life. If you have an Underwood No. 5 in excellent condition, expect it to be worth around $200 or less.
The Value of Unique Typewriters
Older typewriters made by manufacturers such as Caligraph, Hall and Blickensderfer, along with others, do greatly interest collectors and avid typing machine seekers will pay handsomely for them. These are usually examples with shapes out of the ordinary, those incorporating unusual features, or ornately decorated models. Other typing machines made for short periods of time can also be worth more to collectors seeking rarities.
References for Identifying Unique Models
Paging through a reference guide like "Antique Typewriters and Office Collectibles" by Dale Rehr (Collector Books) will offer some guidance in determining if you have a unique and valuable typewriter. You can also do completed item searches on eBay sorted by highest ending price to see some of the more valuable and rare antique typewriters selling there recently for hundreds, and in select instances, thousands. If your antique typewriter looks similar to or is branded like one of those models, you may have a quite valuable typewriter on your hands.
How Condition Influences Value
As with most antiques and collectibles, antique typewriters in excellent condition will be worth far more than those in poor condition. To measure up to excellent status, your antique typing machine should still work and have all its parts in tact. It should be clean and free of marring and dents. Having the original case with portable models also adds value.
For less common models, collectors will overlook some scratches and light wear. In rare instances, a machine in poor condition may still hold considerable value if it's a model rarely found by collectors but it won't be worth as much as a comparable example in excellent condition.