Honestly, anything other than paying market salaries +/- some relatively small error term is probably not sustainable in the long run.
There is absolutely nothing wrong with pricing yourself out of the most expensive market, unless attracting the most in-demand employees (who are concentrated in the most expensive markets) is an existential matter for your company. This actually would let you pay generously compared to tier-2 markets and attract employees that want to leave the most expensive market or who would not even consider relocating to that market.
It is worth noting that the requirements for successfully working remotely preclude most of the lowest cost-of-living locations. eg. it is hard to get decent broadband in the boonies of the desert southwest, or in rural Appalachia.
Edit:typo
Also, remote workers can be more productive, since the average office is full of distractions. (I work with some very productive remote co-workers.)
Price for a week in the office in sf: $500-ish flight, 4 hotel nights $1100, $90 per diem $450, taxis/ubers $30/day = $2k - $2.5k. Throw in a $500 team lunch or two.
I agree remote workers can be more productive; I certainly was. However, I used most of those productivity gains to work fewer hours.
So long as there's an empty seat in the office, it really doesn't cost much to have someone sit there every day. Yeah, there are some free drinks but it's really in the noise and might well be dwarfed by some additional travel for the remotee to come into the office now and then.
However, at some point, having a significant number of remote workers may mean you don't take out a lease on an additional floor or move to a bigger building or construct a new campus, which can be huge costs.
The productivity debate has been done to death and I won't repeat it here :-)
EDIT: And from my experience, 30% of people work more productively remote, 40% about the same, 30% are less productive. That said, there are also productivity losses to in-office people when a smaller percentage work remote, especially if their jobs require frequent team interactions.
For developers it is certainly doable. For other teams it takes a lot of effort for everything to even out. Some companies have figured it out, some have not.
You chose to move, it's your responsibility to cover your travel expenses when you need to be in the office.
Now, if you already live in City B when the company hires you, or the company asked you to relocate to City B, then they should cover your travel expenses when you need to travel to City A.
Your choice to leave, your financial burden. Sure, you can negotiate this as if it were a raise, but be advised that most companies will then simply deny your request to move.
Location is also not really a lifestyle choice in the vein of driving an older car. People have partners, family obligations, etc. in area. It's often not as simple as packing up and moving.
One of the most important pieces in that negotiation is the employee's opportunity cost. "What would companies in your city pay you?" is a very relevant question, especially when most good tech jobs are not remote friendly.
If we see remote take off in a big way, I expect "you live in a cheap city, we'll give you less money" to stop working as remote companies do away with it to attract better talent. That is, unless the best talent stays in the most expensive cities, and like to use that as an excuse for "fairly" getting more salary :)
Anecdotally, I heard this is what Google and Uber did in Pittsburgh.