A PhD is the ultimate leisure class purchase no matter how secure your funding. As a paid PhD student, my earnings are much, much lower than they were in my former professional career. And for the most part, a PhD isn't an entry into vastly higher paying work--especially as a programmer. So, there's definitely an opportunity cost. I'd advise anyone to skip the PhD unless they've got a burning desire to do the sorts of things people do with PhDs, and are drawn to lower / foregone earnings