I think most of the Showcase 4 on ebay have been good buys. The 7.5 and 8.0 both sold for good prices. Ebay is such a pain to search. You would think they would make dedicated search field for comics i.e. title, publishier, issue number, year, cgc, grade, and comments (artist, first appearance, etc). If you have 1-1.5 million listings that to me seems like something worth fighting for. They have not, hence a lot of their business is bleeding off to other sites.
Heritage is not much better. I have a wantlist alert for showcase 4 and I get an email every two weeks telling me my item is available. Unfortunately, it is a Showcase 40 and their stupid search engine doesn't know the difference.