They're hard to find, but not exceptionally rare. I've seen complete BOXED PowerCD systems go for $100-$150 in the past couple years. Recent eBay sales of without-box, looks like it's going for $120-$200. AppleDesign Speakers are also hard to find, but not ultra-rare. They are very nice-sounding speakers (I use a PowerCD+AppleDesign Speakers as my primary CD player at my office!) $50 seems to be about the going rate.
Without original packaging, but with all original cables and remote, I'd say $200 for the set is probably a reasonable price.