I have the Lumix LX3 and love it. The wide angle is amazing and very helpful in cave photography. The lens gives good crisp results. I have only used it on two cave trip and was enough to fall in love with it. Another thing you really want on a cave camera is manual focus. Lumix LX series has this. The Leica D-Lux series is the "same" as the Panasonic Lumixs, slight variations in the camera itself and mostly Leica has some propritary software and more $$. I got my Lumix LX3 from Unclaimed Baggage for about $100. If you scope ebay you should find them between $150-$350 depending on which version you are looking at. I think the LX1 does not shoot in RAW, so I would stay away from that one personally as I find shootingin RAW in caves very nice for easier postprocessing.
If you want an even longer shutter time, Ricoh GX
http://www.ricoh.com/r_dc/gx/gx200/ (there is a GX100, older version, Around $150-$200 on Ebay - stores in the US i have not found to carry them) and a GX200 is the current model. AMAZING camera. 180 sec shutter. And bonus, although propritary LI battery like most these days, you can ALSO use 2xAAA to run it. Of course run time is poor on 2xAAA (like 50 shots or such) but great backup if you are on a long trip and ohshitbatteriesdie. I really wanted this one, actually, but needed a camera ASAP when I was in TAG and my camera busted so had to pick from what they hadat Unclaimed Baggage (which luckily was my 2nd choice and what I wanted before I discovered the Ricohs).
Now if you really want a fancyawesome camera, check out the Ricoh GXR
http://www.ricoh.com/r_dc/gxr/ Interchanging lens system in which the lens is the "camera" itself. At no point ever are the lenses exposed even when changing them. With your budget, it is still likey within it if you fnd it used/on ebay (I see them for as low as $350 with the kit lens on ebay). It is a DUSTPROOF lens system! What could be better for caving?! Sorry still no bulb mode though, wish it had that. Still 180sec max shutter.
Some example shots with my LX3
Macro:
Roppel-Yahoo Cave Pearls 3 by
Sunguramy, on Flickr
Flash gun with some front light:
Roppel-GypsumCoatedWalls by
Sunguramy, on Flickr
Wide angle helpfulness (and panoramic stitching in post-process this is 3 photos)
Roppel-Dome1 by
Sunguramy, on Flickr
Backlighting
Bluff River Cave 14 by
Sunguramy, on Flickr
Lightpainitng
Bluff River Cave 07 by
Sunguramy, on Flickr
To give an idea of wideangle, from Bridge Day, this was ONE shot taken from the tracks.
Bridge Day - New River Gorge Bridge by
Sunguramy, on Flickr