When in the past and even now when people ask what something out of the ordinary costs.
I always ask. "What's your budget for this?" "How much were you thinking of spending."?
From that point on you know whether you are wasting your time, have a real shot at it or what the lay of the land is.
If they say, well I've paid $800 in the past, for example, you'd feel pretty stupid quoting $300 and leaving $500 on the table.
Get immediate feedback. Ask questions. If possible check out their place, and describe what you'd do and get them excited. Then start quoting prices.
Often when you ask questions, you buy yourself time also to get back to them with a quote. You can say stuff like, let me get check what my costs are going to run on this and I'll get back to you.
Michael