The contractor who built this screen porch said he would estimate $90 / SF to build this again, so your quote is not far off his mark. Small additions are much more expensive per SF than large additions, there are many costs that come from mobilizing sub-contractors to show up at your site, and they have to be accounted for no matter how small project. Reducing excavation and foundation costs can be key to keeping small projects affordable, for example.

Hmm, thank you for your response. The house is being built (and ground has even't been broken yet) and the porch would be built at the same time so the contractor is already on site. What is the porch flooring made out of in your scenario?

Concrete slab with slate tiles, beautiful isn't it.

To save money on a screened in porch, a cost effective solution is to used standard size screen doors and build around them.

Thanks for the tip. Yes, the floor is great!