UCLA extension would be a great way to improve your science GPA after a bachelors.
However, make sure that you take relevant classes.
Also, realize that UCLA usually grades on a curve in their lower division and about 1/2 of the upper division classes.
People are super competitive, and it will take alot of hard work to get As if you are taking more than 1 class at a time through extension and with full time undergrads.
Taking classes at csun might be more reasonable.
By the way, I believe it is around 1200 a class for ucla extension.