Why not point at a website and ask how much would that cost? In the sense "I'd like a website that works and looks like HN. How much would you charge to make it for me?"
Maybe watches aren't perfectly analogous. How about walking into a real estate office and asking how much a house costs?
A good real estate agent would sit that person down and find out from them what kind of house they'd be likely to want. So questions like how many people will live in it, how long a commute can you have, how much can you afford, etc will all come into play. And from that info, the agent will be able to show a few houses and home in on what the person really wants.
I remember buying my first house and that's pretty much how it played out.
The point is that the RE Agent takes the buyer seriously enough to figure out if they are just fishing or ready to buy and doesn't just blow them off with flippant responses.
Maybe watches aren't perfectly analogous. How about walking into a real estate office and asking how much a house costs?