BTW, EPGY courses for credit are expensive, but you can get EPGY "school open enrollment" for very little. The downside of school open enrollment is no transcript from EPGY, but if you're in it just for the learning, not the credit, it's fine. (I'm not against credit! :-)) There are various homeschool groups that have signed up as a group to get EPGY "school" open enrollment -- try the Hoagies' gifted forums.
(We happen to use Laurel Springs Academy (a GT program run through Laurel Springs School) and are v. happy with it.)