Then you can take a look at the recent sales of residential homes and compare them to the recent sales of modular homes.
Every area would be different.....and either cost per square foot could be higher depending on the location.
I sold an 8-year old modular home in Northern Virginia last year at it was around $20 a square foot. And in the park where it was, other modulars were going for $25-$35 per square foot.
Meanwhile, single family homes nearby were going for roughly $200-$300 per square foot.
Hope that helps.