June 07, 1999 Got a Million Bucks? Get a Web Site After investigating the average cost for a medium to large firm to build its first e-commerce site, Gartner Group has found the expensive answer: $1 million. By Maryann Jones Thompson After investigating the average cost for a medium to large firm to build its first e-commerce site, Gartner Group has found the expensive answer: $1 million. The majority of the cash goes toward labor costs. The opportunity cost is also substantial; Gartner says the cost of building such sites will increase 25 percent per year over the next two years.