Between $327 and $587 per unit or credit, is extremely common for state universities. You generally have to be resident in the state for at least a year, to qualify.

For example, tuition at Stony Brook[1] costs $6,170 annually. At 30 credits a year (15 per semester), that's $205 per unit/credit.

You'll find that tuition in most state universities are around that range, across the country.

[1] http://www.stonybrook.edu/undergraduate-admissions/cost-and-...