20,000 Leagues Under the Sea is not free, (one of the few Verne books that isn't, because I think the copyrights have been renewed on it too recently for it to be public domain) but it's also not very expensive. However, you have to be careful of translation issues with Verne's books. Some of them are inaccurate, others are just flat out intentionally missing stuff. (that goes for the ones you buy in the stores too) I don't know anything about the German versions, but there are a lot of messed up English versions of Verne's books.
After much research into English translations, this is the one that I got because the North American Jules Verne Society recommends it:
http://www.amazon.com/gp/product/B00...?ie=UTF8&psc=1
It's supposed to be one of the most accurate translations available in English. (you typically want to avoid the really cheap ones) Though, like I said, I have no idea what is available for German translations and if they suffer from that issue. (Google is your friend here, but you can also learn a lot from product reviews)
Like I said on your blog, the Nautilus is looking great so far, Ger.
