There is only so much you can do to seal up a deuce cab against the weather----and if you are in flood waters, you are getting wet regardless... As for costs, if you are diligent with hunting down components yourself (i.e. on ebay, etc.) and aren't against the clock, you could upfit a deuce for $300-400 or less in components plus your time to put it all together. That price doesn't include any other gear you would need to, in my opinion, safely operate in a flood zone. One of my personal deuces is upfitted and in addition to the stuff I mentioned above, I have emergency lighting, reliable comms, flood and spot lights fitted (all add on electronics are at drivers eye level or higher). I also have tactical life vests for my "crew" in addition to some technical (rope) rescue gear and helmets. When I used to do water rescues when living out east, it was our protocol that no truck entered the water without a crew of at least three people-- driver, co-driver, and at least one person in the back who was our "loadmaster" (sometimes we also had ems/police in the back as well depending on the area we were going into). Driver's role was driving only-- coms, manning the spotlights, etc. were all co-driver duties. The loadmaster had the final say as to when we rolled again once we stopped to pick up people (very important-- we had one incident where someone came up to the truck in a small inflatable boat and tied it off to the pass side foot loop on the tailgate without telling anyone-- if it weren't for one of the guys seeing it and shouting for the truck to not move, that guy could have had a really bad day as his line was crossed over his boat from the opposite side and he could have been drug under (it turned out he was under the influence and ended up getting arrested for interfering with our rescue efforts but that is another story). Some people might scoff at that and say how bad could it be for him in only 3-4 feet of water; but then think about what could have happened if he got dragged into the rear wheels.
Remember, every action comes at a consequence (i.e. a cost)--- the key here is to make sure the costs don't outweigh the outcome of the mission. Maybe I am jumping the gun, but I will say it anyway for anyone who wants to help with rescues: know your equipment to the point you could close your eyes and visualize where everything is proportionately to everything else. Know where your contact points are at all times. Try to get a protocol together in advance and get everyone on the same page. And never, ever, EVER, self-deploy.
Z