I have a step-grandson-in-law who finished high school this way last year. It put more of the pressure on him to do the work… and in his case that meant that most of the family had to keep monitoring him to be sure he was doing his four hours a day minimum. He finished and graduated, and was able to move out of town to work at the same time, so I think it was a good solution for him. I think all he really missed was the social interaction and extra-curricular activities, but it was just six months of high school for him… and, frankly, the social interaction was more of a problem than a help for him.
I don’t know about cost, but I imagine that at least some use scholarships, sliding fee scales for low-income students and/or government funding. (If a student is under a certain age, they can essentially be paid like a regular school, though this obviously varies a great deal from one locality to another. WA state has some kind of official online high school program paid for from normal public school funds, though I know little about it.)
A high school diploma is a high school diploma, not a GED. And how many employers really pay attention to the school you went to? Most kids have no choice in their school, and I’ve never heard of an employer favoring different schools like they do with colleges. If the employer is interested in anything, it might be the GPA. But mostly they just want to be sure that you’ve acquired a sort of bare minimum of skills.
I don’t have personal experience with them, but online public school is becoming a thing in northern Michigan, where my parents live. There simply aren’t the funds to have enough physical schools within striking distance of widely-scattered rural homes.