The "best" Japanese blade I was ever honored to handle was a six hundred year old forgery. Very light and short. Very well balanced. Very "tired". That means one more polishing (the only way to sharpen a quality blade) and the remains of the hamon would be gone. It was worth at least a thousand dollars.
Yeah, there are some that fetch more than that.
Careful though, even if it is "old" it can be almost worthless, as there were "cheap" made ones back in those eras as well.