Finding horse trailer values is not as simple as gauging the values of other vehicles. You can try to do it using a list of criteria and a budget and then searching optimistically for a seller who meets both. Knowing values can, however, help with negotiations and also insurance estimates. You have four options: Search print and online ads; ask a trailer dealer; search a limited list on the National Automobile Dealers Association, or NADA; or subscribe to Horse Trailer Blue Book services.
What Others Are Willing to Pay
After spending some time in your search, you'll get a range of values for some models, with some variation based on condition and age. This is a time-intensive method of calculating the value, but the adage that something is worth what someone is willing to pay holds true for horse trailers and is commonly accepted. You can also contact a dealer that sells that make and model, new or used.
NADA and Blue Book
NADA only lists values for horse trailers with living quarters. Select the RV heading on the NADA website. At the bottom, click on the "Travel Trailers/Fifth Wheels" option to get a list of manufacturers. Horse Trailer Blue Book charges subscription fees for access to values covering 1993 through 2013 models. Subscriptions begin at $9.99 for 24 hours of access.