You can't go wrong with any of the dslrs really, they'll all give better pictures than a point shoot owing to the larger sensor size. I'd check out the lower-priced Nikon or Canon DSLRs on dpreview.com and also read their DSLR buying guide under the "buying guide" menu. The Nikon D60 or D90 would be good choices with Nikon and for Canon, the EOS Rebel xs or the newer 500D. You'll get better deals on the somewhat older models with "only" 10 mp or less, but these could be in the 500-600 dollar range.
My favorite flashes by far are the Vivitar 283 with the optional VP-1 power dial that lets you go from full power to 1/64. Most other flashes that let you do that are big and bulky. Get them used on ebay and buy the VP-1 adaptor new from bhphotovideo if you don't see those on ebay. rarely you will see a 283 listed that already has the adaptor.
Tripod: Some of the slik series are pretty lightweight or for ultimate cave adaptability (but not lightweight) the Benbo Trekker 2. But get slaves like firefly or Wein hs-xl and you won't need it very often.
pelican and otter cases that fit the slr will be pretty bulky. I carry mine in one of the small plastic kegs that every European caver uses. White with a big red lid, big O-ring, lightweight and reliably waterproof as I've found again and again. Just make sure the lid isn't bumped in your pack while crawling, this loosens it. It has small holes you can use to wire it securely shut. I think IMO carries these, if not, canyoneering places do.
NSS News Editor