The cost of a "real" ninja sword can vary widely depending on several factors, including the sword's quality, craftsmanship, materials used, historical significance, and market demand. It's important to note that historically authentic "ninja swords" are rare, as the term itself is more associated with popular culture and fictional portrayals rather than historical reality.

If you're referring to modern reproductions or replicas of swords that are often marketed as "ninja swords," prices can range from around $50 to a few hundred dollars. These swords are typically mass-produced and may not necessarily adhere to historically accurate designs or craftsmanship.

However, if you're seeking an antique or historical Japanese sword that is associated with the shinobi (ninja), acquiring an authentic piece can be quite challenging and expensive. Genuine antique Japanese swords, including those with historical significance or lineage, can command high prices, often starting in the thousands of dollars and potentially reaching significantly higher values depending on their rarity and desirability.

It's important to exercise caution when purchasing swords marketed as "ninja swords" and do thorough research to ensure authenticity, quality, and accurate historical representation. Consulting with reputable dealers, collectors, or experts specializing in Japanese swords is recommended to obtain reliable information and guidance regarding pricing and authenticity.