We're not going to put a number here that doesn't belong to this job. Cost depends on the horsepower you need, whether the existing rail and bracket can be reused, and whether the header needs reinforcing - all things we confirm on-site, not over the phone.
What we can say: Old Greenwich runs noticeably higher median household income than the rest of our Stamford service area, and in practice that shows up as more owners choosing belt-drive or smart-enabled openers over the base chain-drive unit, since the price difference matters less here than the quiet and the phone control. That's a pattern, not a quote - your job gets priced on what's actually in your garage.
For the general cost breakdown across the service area, that's covered on our Stamford opener page, not repeated here.