I have gone to some trouble to research these and I am requiring specific texts because of the extra materials they offer. I know that they are expensive, but they are essential for the proper operation of the course. If expense is a critical issue, get in touch with me. You can probably space your book purchases out throughout the year; you may even be able to buy used copies of some of them if you are vigilant (and if you frequent used book stores a lot) or if you get in touch with one of last year's students who is willing to sell you some of the texts (a few have changed). A glance at the schedule will let you know what's coming up. You can probably rationalize the cost and volume to yourselves if you consider that this is reading for the equivalent of a year-long college course. (That's two semester courses, or three quarter courses. Whether any college will really give you that much credit for it is another matter — that varies greatly with the college.)
The titles are listed at the Scholars Online Bookstore Site.