I have to recommend the correspondence course I'm taking. It's "Astrology: The Cosmic Pattern" by Joanne Wickenburg. The course is in six units, and you can pay for one unit at a time. Each unit costs $80 U.S., and consists of five or six one-hour lessons on cassette tape, plus workbooks. There are homework assignments (multiple choice) to send in to Joanne, who will correct and return them. The course is very comprehensive, covering introduction to planets, signs, houses, aspects; chart calculation and construction by hand; introductory, intermediate and advanced chart interpretation; and transits and progressions. She has separate units for solar return charts and horary. After spending much time researching correspondence courses, I can tell you that this course is among the best in quality and is certainly the most cost-effective.
http://www.joannewickenburg.com
-- Lee