I just added two tags to the site: cheap and bundle.
Bundle is pretty self-explanatory: it marks a series that has a bundle of multiple ebooks available for one price.
Sometimes these are a really good deal and well-formatted; sometimes they are not. So you may want to check the comments before you buy one.
Cheap needs a little more explanation. I’m using cheap to mean that every book (not including any anthologies that contain stories) in the series costs less than $5 in ebook form.
As I mentioned earlier, I am starting to check out the really cheap ($0.99 to $2.99) UF/PNR books and finding some good stuff, but for the moment $5 seemed like a good cut-off.
But remember to check the price before you hit the buy button. I don’t think I tagged any series with short-term promotional prices, but I was doing this by hand so I may have missed something.