I just went through all of this myself.
Im a superintendent for a large general contractor so i chose to GC the job myself. I bought the package, windows, doors, etc and basically bid out the build.
For reference my building is 48'x64'x16' with scissor trusses. A mezzanine thats 16' x 48 (upstairs bow shop, downstairs future mother-in-law suite).
For just the core/shell, insulated, mezz framed and sheeted I'm into it for 103K. Add power (main service), dirtwork, plumbing, mechanical, electrical, concrete, permit fees, engineering, etc. ill total out somewhere around 170K. The mother-in-law suite ill fit out myself for relatively cheap per SF.
I got prices from Morton, and 2 other builders around my area and could not justify their prices for a post frame building.
Thats my 02. I'm located in Elizabeth Colorado if that helps any.