It really depends where in US. $60k/yr in NYC or SF or Seattle will be hard -- you'll need to get housemates to share the costs of housing. But $60k/yr is some small town in Vermont or Montana is comfortable in my guesstimate.
Does comfortable mean being able to find specialist doctors? Or even just enough doctors? Being able to eat a variety of fruits/vegetables year round? Constant supply of avocados? Being able to live near family? How secure is one's income, or how many possible buyers are there for what you are selling? How are the schools for one's kids? Will the school community be of acceptable quality?
Of course, these answers will vary person to person.
One thing to keep in mind is that you might $100k+ in student loan debt by the time you actually get your phd. So for that reason you go for the higher paying job.
The lowest salary offer I got on my faculty job search, with an apology re: salary bias against folks without clinical degrees, was half again what's quoted there.
There's certainly an argument to take a pay cut to do a PhD if you enjoy doing it.
The thing is - go ask real PhD students 2 years into their PhD whether they're enjoying themselves. Given the 50% drop-out rate, you can probably guess what the answers will be...
If you believe this is accurate 60k is doable, 30k is not.
I doubt you could do 38,169 without a roomate.
In other words, what's the actual, practical need for a person (or a smaller nuclear family) in the US to actually earn $400k a year?
Similar to the US, university-employed PhDs definitely tend to make less than many industry professionals in my country as well. Then again, it is nonetheless a very acceptable standard of living. As civil servants, life is very stable (as compared to e.g. one-person companies), and they are by no means poor. Most importantly, though, a doctorate program will very probably train you into a better, more analytical thinker (I've seen very few examples of the contrary).
For that reason, I've always found it questionable when PhD vs no PhD is debated solely on the basis of expected income. Maybe I should remove my pink glasses, but there is, still, a little more to it, isn't it?