Affordability is in the eye of the beholder, but this course, offered every summer at Steward's Draw PDC at The Draw in northern Wisconsin, probably fits: $450 for the ten day course with an excellent instructor, Nat Larson. This is a course for those who don't need a stamped and signed design certificate, just all of the learning. Yes, it includes camping and meals. And it starts next weekend! Their phone number is on the website-- much faster than email, which usually takes a week or two at their internet-less farm.
I have visited their permaculture farm several times and am in awe of what they have accomplished in seven years. I've also taken two classes with Nat and his sidekick, Eric Frank, who runs Bay Permaculture . They were outstanding, given here in the driftless region of SW Wisconsin where we also have classes given by Mark Shepard. I recommend both of their classes heartily.