Liberty Mutual spent $4.5 million to renovate a 1,335 square foot executive suite that was, in all likelihood, working just fine a month before. It breaks down to $3,370 per square foot, making it perhaps the most valuable real estate in Boston. Put another way, the renovation cost is equal to what a $100,000-a-year worker makes over the course of his or her entire career. It took the former Liberty Mutual chief executive, Ted Kelly, a full month to make that amount of money, that’s how high it is.