JWO...Just trying to get a handle on this.
Possible options as you presented it.
1) A lady wants to sell the bike, has no idea of value, and has asked you to estimate its worth.
2) A lady wants to sell the bike, you want to buy it, but have no idea of value and what you should pay.
3) A lady wants to sell the bike, you want to buy it, but have no idea of value and what you should pay. So with a vague description, other than it is a one off, you ask the Forum Members to value the bike, unseen.
The answer is that the price paid is the monetary value when cash changes hands and buyer and seller are agreed. The cash value depends on who is buying, who is selling plus the other variables....desirability, rarity, utility, condition, negotiating skills, desperation, e.t.c.... you name it.
If you are buying, you know in your own mind what it is worth to you, and what you are prepared to pay. If you have been asked to value it, and you have no idea, then politely decline, leave it to someone else to sort.
At least our favourite online auction site gives a live insight in to the real world of buying and selling, so at the end of the day that is one place where you can easily direct your research.
Hope this is of some help.
Swarfy.