Ripping 700 CD's to HD using FLAC-How much space?

700 CDs will take up less than 300Gb. That's about what I've got.
I'm using two 500Gb external HDs right now -- one for the music, one for backup purposes. As you said, drives are cheap these days, so I may purchase another one as well.
I'm considering a NAS as well, but that may be overkill for my needs.

Zowie:
It's a valid question for sure. Why not save everything as .wav (uncompressed) files?

There are a couple of reasons besides saving space that I use flac:
- The wav format doesn't have any set of agreed-upon ways to store metadata. I always seem to lose metadata whenever I convert from one format to another, or switch from one player to another when I use it. That's not an issue for flac or aiff or wma.

- I think Squeezebox transmits everything in flac format, so it's helpful to have it already compressed so it doesn't have to compress it while streaming.

- Drives are getting cheaper, but bandwidth is not necessarily keeping up. I use a small Passport USB drive at work which at 500Gb can hold all my CDs for now. My music skips a bit if I do anything else that accesses that drive while I'm listening. Using flac cuts the data rate in half or so versus .WAV files, which lowers the USB contention on my laptop, and makes my drive happier.

Regards,
Jonathan