Some districts also have night classes.

Also see if there are any charter schools in the area. They are generally free. You just have to really check them out closely to see that they have a "decent" student clientele. Unfortunately, sometimes they are filled with students who couldn't follow the rules in their school district and they are using charter schools to dodge disciplinary action. But they aren't all that way. You just have to do your homework.

I know there are some computer-based homeschool programs you can enroll in on-line that might be a good option for a high schooler. Personally, I'd have trouble homeschooling a high schooler in math, for instance, and probably would be doing them an injustice without some more expert mathematics help. Seems like my sister-in-law used some sort of on-line homeschool system for her boys once they hit high school age.