Are you looking at the Sound Devices 722 for a specific reason rather than the Sound Devices 702? You REALLY don't need that kind of storage. An 8GB CF card will last you for at least a day for sure, even several. Plus, do you really want to have all your sounds on a huge drive, ready to get corrupt from running around chasing sounds or stollen from being in sonically awesome places but maybe not so safe? Better to have solid state (like a CF card), and backup everyday.
Now the other main thing about a 722, is that it has timecode. You say you mostly want it for field recording and maybe some production audio, so chances are you don't need timecode.
The cool thing about the 7 series, is that you can lock several machines together, so they're all in sync. If you want to turn your setup into a four channel, then just buy another machine and link them :-) That's what I did. Got two 702s, and if I need to have four tracks then I connect them and if I need to have them separated (SFX or line feed or a second recordist), then I can. Obviously you can get a mixer as well...
Does $1,800 (702) seem better as a price tag than $2,500 (722)? If not, then there are a ton of other options out there, and we can cross that bridge later on.