I'm currently working on a major remodel/ addition in Hillsborough, and bid out the project to several contractors. The project has a modern sensibility with a fairly high degree of detail and finish. The new area, consisting of remodel and addition, amounts to 3500 s.f. and the price ranged from $1.4 mil to just under $750,000. The contractors that put in the low bids did not include decorative light fixtures or finish material, i.e. tile.
Be aware that the Town of Hillsborough has a design review process that one has to go thru...the more complex the more difficult it gets. Modern designs take a little more scrutiny but there is a slight trend in going this way...the last hearing that I went to all the project under consideration were contemporary style.
Hope you find this information useful.
I'd say on average you could use $400/ft as a benchmark for minimum Hillsborough quality work including demo, plans, permits with it going up for finer details and a custom owner user quality or down a little for spec resale quality?