Check with your local community college to see if they have a program. The college in our area that offers this was a 2 year college, but is now a 4 year state college. When we lived in North Carolina they had a similar program.
All we had to do was register with the dual credit office. They registered him and waived the registration fee, then they sent him to take the College Placement Test.
In order to take classes they must qualify to be in College Algebra (we used Saxon Alg. II and he qualified with no problem), qualify to take Composition I (this also didn't seem to be a problem, he qualified for Honors Comp, I used Abeka grammar in our homeschooling), and qualify in Reading Comprehension at a college level.
So now he's free to take whichever classes he chooses, up to 15 hours per semester.
We're working on the General Ed requirements, because at this point he doesn't have an inkling as to what he would want to major in.
But the way I look at it, we can get all his Gen. Ed requirements out of the way, for free!!!!
The community college can also be a good source for foreign language instruction. My wife teaches such classes and has some homeschoolers as well as usual college age students, even retirees. The courses are also available on the Internet although not for homeschoolers.
Our local community college allows homeschoolers to take classes, but it is certainly not free. They pay $115 per credit for the courses. But it can be a bargain because that is certainly cheaper than the State colleges, so taking a few courses before you head off to a 4 yr. college helps lower the overall tuition bill.