re: Builder Asking About Budget on House?

It's like anything else. There is an inherent conflict of interest/moral hazard, and the more knowledge you have, the better chance you have of minimizing the moral hazard. We face it dropping our car of at a mechanic, and you face it with real estate agents and all points in between.
This is a huge purchase, so it's wise to get information, or at least and advisor who knows what they're doing.

Good info and suggestion

What about doing self contractor ? Do the research on materials and you call and make the material purchase instead of the contractor doing it. Doing this will allow the self contractor to shop price comparison instead of purchasing from same supplier. Yes this will take more time but if cost savings is your intention then doing the homework is key.