For a casual fan of stright ahead, I think the Seven Steps box is definitely your best choice. The 65-68 is the best music (ever made) but its really not very easy listening. easier than Bitches Brew of course.
Your best bet would be to order the box from www.yourmusic.com 5.99 a disc, so the Seven Steps would be 42 dollars, which is practically free. It should only take a week or so to arrive.