I'm in Bergen County, NJ. Housing costs and property taxes are high of course. But once that nut is cracked, what else is higher? Cars cost the same everywhere, groceries cost the same, and at least here in NJ gas is actually a bit less than many other states. I suspect services like a plumber or electrician are higher, but probably not by much.
My "number" is....good enough. DW still w*rks by choice. When I ER'd, we looked not just at our numbers, but also our lifestyle. We take 2 nice vacations per year. Beyond that, we enjoy the occasional Broadway play, day and single overnight trips, and driving to various bike paths to bike.
So, our "number" is more than sufficient to support the lifestyle that makes us happy. And, we don't see us changing that lifestyle, which was why I could ER with 100% confidence.
Don't just focus on the amount you need to amass, but look at your likely expenses and the aforementioned lifestyle. Living in a so-called high cost of living area may not be so high cost for you.