In Kansas City, most composite deck builders charge $90 to $120 per square foot installed, including the substructure (joists, posts, and beams) stairs and railing. The height of your deck, style, design, options and material choices will all affect your final cost per square foot.  A 200 square foot composite deck with stairs and aluminum railing, for example, would cost between $18,000 and $24,000 from a reputable, licensed and insured decking contractor in Kansas City.