Where to find?

I originally read The Circle of Magic and The Circle Opens books when I was just a young girl in high school. I want to say it was sometime around 2000. Now in a mother of three and I'd like to share these stories with my daughters because I loved them but also because of what inspirational stories they are.

I've found a few "sets" online but all of them are either in poor condition or far overpriced. Does anyone know a good site where I could just buy the whole series (I never even read beyond the second set myself so I'd love to find the rest as well)? Any help would be greatly appreciated.