I have also been reading a lot of public domain titles and some library books. ePub support is why I bought the Nook over the Kindle.
I also did research the cost of books. The problem I have is that I believed articles like the one referred to by a previous poster. The reality is that the books I tend to want to read (non-fiction for myself, child and young-adult fiction for my daughter) have consistently been higher than what Kindle editions cost.
The real 'answer' for me is going to be library ebooks but the selections are still a bit constrained at the libraries that I am able to use.