I don't know their rates or how exactly they've been working with clients recently.
However, there's sizeable demand (and not nearly enough supply) for that kind of high-quality dataviz work. There's also nothing that'd inherently require this work to be done non-remotely. Quite to the contrary, this kind of work particularly lends itself to being done remotely.
Knowing the tech (mostly D3.js and Processing) is only one, small component of a successful career in that field, though.
Having seen quite a few of Nadieh's (and similar data visualisation designers') talks I'd say that design, UX, an understanding of art and a creative imagination are just as important, probably even much more so.
PS: You might also want to check out Mike Brondbjerg's work: http://www.kultur.design/