I agree with DVS on this. Certainly for a simple little project you could price on the spot, but I never do. I will give them a ball park range since I know what our price per square foot on our most common pavers are, however; that price is never the same. When I bid pavers and landscaping, I never use unit numbers. Its always bid per job.
Example, we did a 200SF walkway for a customer where everything could be accessed with our skid to bring materials etc. I was able to install that walkway for a hair under $15/SF with hollandstone. A week later I went and bid a patio extension using hollandstone where all the materials needed to be brought down by hand, no machine access what so ever. That one was closer to about $22/SF becasue of that. So certainly I will give a price range to a customer on the spot, generally its always about 1500-2000 higher and see how they react.
And I think its probably easier to say having more like 150-200k on a hardscaping job in equipment
Dump Truck and Trailer to move equipment/material 75-100k