Wow $40 per sq. ft. I was going to say why don’t you wait and buy an existing house. The $16 per sq. ft for additional construction tasks does sound low. Of course it depends on the level of complication of the site work mostly but $16 may get you a foundation and maybe a little more unless you are doing it yourself or with unlicensed people.
Don’t forget plan check, permits and other fees like,parks,schools, water meter, sewer, fire dept. etc.
There are some very nice modular homes in the semi-rural area where I live. It seems like a good idea.
I am not sure how this will playout but my experience shows that even the best modular home dampens resale as compared to custom site built. Maybe that is changing? If economy to build and own guiding factor I wouldn’t worry about this at all, not with the prices you are talking about and the questionable market we are in.