Building interior window insulation panels Cost: $1.25 sq/ft -Price based on common lumber prices at stores like Lowes. Can be even less if using cheaper bought wood. Commercially made products cost $9 sq/ft Time: 2 people, 40-45 min per window frame Avg. savings for harsh winter climates: $4/$10 per sq/ft of window. Page includes more specific cost savings calculator. Able to be removed in summer months.