sun, why don't you stop over to the "Acoustic Music" forum and repost your question there? I think you'll find a lot of interesting feedback and ideas there as well.
Personally, I've had great success with a pair of good omni's for the room sound (with a solo classical flute) and a close up mic for detail, etc. FWIW, I wouldn't go with two cardioid mics on a solo instrument for "Stereo", I'd use the omni's for the overall soundstage and mix in the solo/spot mic front/center for a little detail. Also be aware of what it will all sound like in MONO. Granted, just about everyone listens in stereo, but it's just good practice to make sure it all folds up nicely into mono whenever you encounter it. (Table radios, cheap TV sets, etc.)
I conducted my own "shootout" with a vintage KMi-84 and AT 4050 on the flute, and (this time) the AT-4050 won out for overall warmth and a little less breathiness (which was actually a bit surprising to me.) The KM-84 always beats EVERYTHING I put up against it, but this time the AT won out. (It was also a VERY good recital hall as well.)
I mixed the spot mic with the omni pair and got a great natural blend of it all.
You can get a decent pair of C-4's for under $400 (from Studio Projects) with BOTH cardioid and omni capsules. They're not DPAs, but they'll get you started for your budget. Use them for the omni pair, and then get one of the large diaphram mics we're all talking about for the rest of your budget: AT-4050, 4060, etc.
Good luck with it!