Value, and rarity, are not dependent.
Rather, "value" is inexorably tied to the concept of desirability.

Eg.,
I could personally build a one-off rattle canned gas pipe road bike with 20" steel wheels in my basement...
- If rarity were the determinant, its being one-of-a-kind would make it far more valuable even than your 1950 Hetchins Experto Crede.

(Let me know if you disagree, and I'll start taking orders)