The average cost to repair or replace stairs is $1,000 to $2,000, including materials and labor. Staircase repair costs are influenced by design complexity, material choice, labor rates, and stair shape. Common stair repairs include painting, carpeting, and structural improvement with specific material types.

Simply cut the rotted or termite damaged materials out of the stair stringer and replace it with new lumber, possibly treated lumber if you think that will work better.