Atom should be priced at what it's worth, based on what the market will bear and what the developers' time costs. For people willing to pay for their editor in the first place, $60-70 isn't particularly out of the question. As much as they're a force for good in the open source world, GitHub is still a business and I'm sure they're looking to be rewarded for the time and resources invested by their staff on this project. As we've already seen in a few places in this thread, people are willing to shell out plenty of money for a good editor.
GitHub has a pretty good relationship with students, so we might see a specially-licensed or otherwise qualified version for student use at a discounted price, but I suspect most of us are looking in the same ballpark as Sublime Text, RubyMine, etc based on @mojombo saying it will be "competitively priced". For me personally, that's well worth it.
Users who can't afford that sort of pricing still have plenty of other options, from open source editors to nagware like Sublime. They're not obligated to price it in a range that makes sense for absolutely everyone, because I don't think "world domination of text editors" is on their road map, and because there are some people who'll never pay for an editor no matter what the price is.