It is my general impression that most "hackerspaces" cater to the more general definition of "hacking" (building, electronics, software, modding, including arduino and similar devices), while most of the "hacker conventions" are more geared to the security-minded subset (cracking, privacy, etc.) There is of course overlap, but I wouldn't expect CCC to have a lot of interest to the general Arduino community. See this list of 2007 talks, for instance: http://events.ccc.de/camp/2007/Fahrplan/track/Hacking/index.en.html
I've never been; the whole security arena is a big turn-off for me.
2007 was about 150 euros (about the same as a good-sized science fiction convention, and MUCH cheaper than the average commercial for-profit technical event. But more than a Maker Faire.) Depending on where you live and how you travel, I'd expect travel, food, and lodging to be the major part of your expenses.)
I'm getting all this from the web; have you watched the videos describing the previous CCCs ?