A good trail horse costs $3000 or more. However, don’t expect anything more than $5000 even for the priciest option. A horse of this price will be definitely one of the best horses for mountains. It will be obedient, physically strong, good at taking commands, and might even come with a bonus of trail riding experience. You may find cheaper options but those horses will probably be younger. A teen trail horse is easily available for $1000. Unregistered trail horses are also lower in price.