https://www.bestplaces.net/cost-of-living/spokane-wa/seattle...
https://www.bestplaces.net/cost-of-living/spokane-wa/seattle...
That sort of cost of living also doesn’t account for a huge amount of other things too. Having a holiday in Bali costs the same whether you depart from Spokane or Seattle (probably slightly more departing from Spokane actually, when you account for transport from Spokane to SeaTac). Buying a new 4K big screen costs the same in Spokane as it does in Seattle. Living in Spokane doesn’t make your kids college cost less either.
But then it fails to take into account the percentage of income that actually goes towards housing. If you make 200k and move to a place where the primary difference is housing costs (say 2x housing costs), the adjustment should be up to about 250k (assuming housing ~25% of income), not 400k.
It would depend on how much of a pay cut you experience moving to Spokane, but that can certainly make colleges with extensive need-based aid cheaper.
Other costs are not much higher if at all. If you go to a bar in the financial district, that's usually a business expense so it's justifiably expensive. It's this way in all cities or towns with a large enough center though, so pricing come out somewhat equal. It's when you compare city center prices with outskirts of city prices where the difference starts to matter more.
Spokane and Seattle are on opposite sides of the state - 280-300 miles apart. I don't get what you're trying to get at. The distance is large enough to go through multiple states on the east coast. I don't think it's really an apt comparison since the two are nothing like each other. You could make this same comparison in CA with a SF Bay Area salary and even less distance apart. Here's one for you: https://www.bestplaces.net/cost-of-living/redding-ca/palo-al...
All that matters is that Facebook consider them within the same CoL-adjusted region. If their CoL weighting is applied at the state-level (for example if Washington residents are to be paid at 80% the effective SF salary), then this is the real arbitrage.
Having that grid information would be very useful to an individual when negotiating.