Have you looked at hiring a cd ripping service like MusicShifter? A lot of these places will rip you collection for cheap because they have massive digital libraries of pre-ripped music. Once they receive your cds instead of actually having to rip all 300 of them there is a good chance that 250 or so are already stored in their library resulting in a relatively cheap and fast service ($.79 per cd from Music Shifter).

(I'm in know way affiliated with any cd ripping services - I've just heard good things about them.)