I have tried several educational options for my older son. He's attended private and public school, we homeschooled, and he took distance education courses.
It's very difficult to determine what an "all over the place" kid needs from his education. Because of this, I view homeschooling as the ideal option. Unfortunately, doing this without a support group is like doing trapeze without a net (almost). I spent a lot of time reading the Mensan Homeschooling discussion group on Yahoo, but there was no one locally with whom I could swap notes. This was isolating for my son as he had very few friends.
Curriculum as a homeschooler is very fluid, but I found drawbacks to almost every method. I remember a year of homeschooling where I came up with a lot of matching games for him to play in order to learn facts from the "What Every Nth Grader Needs to Know". He enjoyed that, but it was very time intensive for me.
We tried boxed curriculum. My son devoured everything related to English and History in a couple weeks but would not touch other items. I honestly don't feel it was a waste because he did spend time reading good quality books, but we didn't use about 3/4 of the materials.
Distance education courses were good both because the content can be chosen for the appropriate level and they tend to be clear about expectations. The big drawback to these is their very high cost.
The process of finding the "correct" curriculum can be both time-consuming and expensive. I'm sure, however, that this is cheaper than private school and probably cheaper than public school. Public school requires parents to buy materials, lunch tickets, bus tickets, gym clothes...and then there is all that expensive testing that must be done to show that you do have a gifted child. As far as testing is concerned, you get what you pay for.