Costs to build 5 duplexes

[Horace Mann]

I have an opportunity to purchase land currently zoned and approved for 5 duplexes (or 8 SF).  It is 3 miles from a university and I am thinking of building student rentals, (doing the 5 duplex option).  My commercial lender has funded a similar project in the same town.  4 bedrooms each side, with porches and garages at $170/SF.  Does this sound like the cost for an investor like me to build and hire a GC, or does it sound like a GC's cost who is building/GCing it himself without a markup added?  I want to have a general idea before meeting with contractors in case this is $50/SF under what I would have to pay to hire a GC, because if so it may knock me out of the deal.  Hopefully I am articulating my question clearly. Thanks for your thoughts on this!