From Cost -vs- Value Report published in Remodeling Magazine by Hanley Wood Publications
FAMILY ROOM ADDITION
In a style appropriate to the existing house, add a 16-by-
25-foot room on a crawlspace foundation with vinyl siding
and fiberglass shingle roof. Include drywall interior with
fiberglass insulation, pre-finished hardwood floor, and 180
square feet of glazing including windows, atrium-style
exterior doors, and two operable skylights. Tie into existing
HVAC. Add electrical system to code, including 12 recessed
ceiling lights.
The Miami FL average price for that project inclusive of labor, materials, permits and a small contingency fund is pegged at ~$79k or about $200 / sq ft