The Volunteer
Marine Rescue service conducts low cost courses, including
navigation. For your purposes these would be ideal.
Not all branches conduct these courses, so depending on your location you may have to travel to one. Central Coast is one that does.
Although not specifically on
navigation, another excellent and inexpensive resource is the book "How to Read a Nautical Chart" by Nigel Calder. It covers a lot more than the title would imply.