Can you find an identical unit elsewhere (perhaps one with a broken display or other damage) and swap boards? Even if the system you swap with isn't working, as long as the system board is ok, you should be fine. Latitude system boards are very easy to swap out, so I can't imagine that Inspiron would be that much different.

$600 for a brand-new lappie board isn't that bad actually. I got a repair quote for a Sony Vaio that only needed cosmetic work, and they wanted over a grand. I can only imagine what they'd have charged for components!