The cost of a trombone is going to really depend on the condition, the brand and the type of trombone you are looking to purchase. On average, the prices of a trombone can range anywhere from as little as $300 to as much as $9,000. For example, alto trombones can retail for $300 to $4,000 while a small bore tenor trombone can cost $700 to $3,500 brand new. On the other hand, medium or large bore trombones can retail for $1,500 to as much as $5,500.