Briefly, Tokuno sensei states that he places a value of 100% on katana which are ubu, zaimei, with a genuine signature, of excellent quality and condition, and of length 2 shaku 3 sun to 2 shaku 5 sun.
1. Katana around 2 shaku 1 sun, plus or minus, are worth 70% unless they are sue Bizen katate-uchigatana, which are normally about 2 shaku 2 sun.
2. Long wakizashi (1 shaku 8 sun to 2 shaku) are valued at 40% to 70%.
3. Medium wakizashi (1 shaku 5 sun to 1 shaku 7 sun) are valued at 30% to 50%.
4. Hira-zukuri ko-wakizashi (1 shaku to 1 shaku 4 sun) are valued at 40% to 60%.
5. Tanto (less than 1 shaku) are valued at 30% to 60%.
6. Yari and Naginata are valued at 20% to 50%.
7. Blades with non-typical sugata are valued at 50% to 80%.
Further, he states that before the war, swords longer than 2 shaku 6 sun were valued at wakizashi levels because they were impractical for use, expensive and difficult to polish, etc. Presently, since swords are now appreciated rather than used, this no longer holds true.
He also mentions that each sword must be appraised individually and that his prices are just a general guide.
As Jean has touched on, I think it is clear that more value is placed on blades that were most likely actually carried and/or used by samurai, not the merchant class.