Hello Lisboa
As stated above, the main free place to get Portuguese eBooks is project Gutenberg (
http://www.gutenberg.org/browse/languages/pt).
Of course these are books that are out of Copyright (by Portuguese law 70 years after the death of the author), so mainly the 9th century Portuguese classics (Eça, etc…)
Another example is eBooksbrasil (
http://www.ebooksbrasil.org).
As you should know, modern commercial eBooks in Portuguese are almost non existent, just in the end of last year publisher Leia begun an eBook selling space in their online library (
http://www.mediabooks.com/catalogo/?t=ebooks).
Not much to choose from, but they cost around 70% of it’s paper counterparts and if one buys the paper book and the eBook too, pays more 2,49 euros for it (
http://www.mediabooks.com/faq/?faq=4).
Best regards,