My suggestion is to buy a 15 foot or smaller very cheap dinghy that's pretty beat up, but serviceable. This is not going to be a boat to take your friends out on, but instead you will be crashing into docks, running aground and even tipping her over on occasion.
This is how almost every professional sailor of note learned to sail, not through some cookie cutter expensive course.
Along with your little beater, I would highly recommend a great little book called Royce's Sailing Illustrated, a fun yet very comprehensive book filled with information for the novice sailor or experienced professional. No massive preachy tome this, just a well put together book with everything from rigging, docking and even splicing. I've been using it to teach sailing for nearly 45 years.
Good luck and remember, sailing is supposed to be fun, so keep that in mind when you are having a hard day.