The cost for dual enrollment at our local community college is 1/2 regular tuition per credit hour.
They do dual-enrollment here in Pasadena CA too. If the student gets a B in a class, he gets an A as a high schooler. Many homeschoolers, however, just enter the Jr College at 15 or 16 and get on with college. Our homeschooler did. Our homeschool ‘umbrella school’ issued him a diploma/ no problem. Age 18 is not a magic age for that.