E.G. if living in Manila is 50% cheaper than living in SF (http://www.expatistan.com/cost-of-living/comparison/manila/s...) (and my apologies to gdiocarez if they don't live in Manila!) you probably shouldn't price yourself at 50% of the wage of a US remote worker. But what about, say, 5% cheaper than the competition so that you can compete on price (or indeed earn more, relatively speaking) without devaluing your skills?
I think current advice here does a good job of giving you some algorithms for taking your cost-of-living and working upwards to a reasonable wage from there.
(Full Disclosure: I've worked in Waterloo, Canada and currently in London UK, so I'm used to a generally lower salary than comparable jobs in the US and currently pay similar living costs to SF and NYC. :P)