cost per foot for building duplexes

We are looking to team with a builder to add a 2700 sq ft duplex on a recently acquired lot.

What is the standard rate (roughly per foot) we should be charged/can expect for the finished project?

We’ve heard $80-100+ is common, but based on what he’s asking, it would kill our cash flow in the area. It’s in the North Texas area.

Thanks!