Why is Wolf's Rain so ridiculously expensive? I am looking to add the complete set of Wolf's Rain to my anime collection, however after shopping around on E-Bay I see the following:

Wolf's Rain for over $300

This is a pretty common price-point for Wolf's Rain, I constantly see that this series is starting at over $300. Why is this? From what I understand Wolf's Rain was never really a huge hit. So why does it cost so much to obtain a legitimate copy?
You're looking at the original run of Wolf's Rain, which is no longer in production, and as such is subject to secondhand supply and demand price increases.

I recommend that you look into the Wolf's Rain - Complete Collection Limited Edition DVD Set released in 2005. This set started at 149.99 and is listed on the related auctions on the link you provided to eBay for $195, a ~25% increase from its original price.