DLR, your best bet is to use a cave dive light canister. My instructor has been down to 600fsw (Edmund fitzgerald)with them, I've been to 200fsw and my buddy has been to 400fsw and on the Andria Dora with his. Check Dive Rite ( http://www.diverite.com/catalog/lights ) or Halcyon ( http://www.halcyon.net/lights/video_hmi.shtml ) or any canister making companies and plug where the light goes in. You can make your own but I have an old AUI one yhat I've used for years and never changed the seals (Stupid on my part) but never had any leaks (knock on wood).
A lot of the Tec divers using OMS or other equipment ( http://www.omsdive.com/misc.html ) put in there empty cave canister a portable life ( http://www.halcyon.net/mc/dlr.shtml )a cell phone, radio, dive alert, dye markers and tube ( http://www.halcyon.net/mc/dam.shtml )and a EPIRB as well as portable water and a couple of power bars in case they get lost at seas. So it depends on your flavor, but if you are or presently in technical, I would use cave diving rescue equipment. The Dive alert and the tube marker has saved my life once from a lost boat due to high currents and a anchor line break. I do more cave diving than technical wrecks, I like a little more control over my elements.
And if you need O2 (Oxygen), just as your taught in class, go to a welding store and rent a bottle of Aviator Oxygen and put them in your O2 cleaned tank and seals because we all know Aviator Oxygen is more Pure than Hospital grade Oxygen and you don't need any requirements to get aviators oxygen but you may for medical and medical oxygen is not as purer anyway.

Also check Ebay as well ( http://listings.ebay.com/_W0QQsocmdZListingItemList?sofocus=bs&sbrftog=1&fcl=3&socmd=ListingItemList&catref=C3&from=R2&satitle=&sacat=29575%26catref%3DC6&sargn=-1%26saslc%3D2&sadis=200&fpos=ZIP%2FPostal&sabfmts=1&saobfmts=insif&ftrt=1&ftrv=1&saprclo=&saprchi=&fsop=3%26fsoo%3D2&coaction=compare&copagenum=1&coentrypage=search&fgtp= )