Inexspensive water? preferably clear.

Check out the floral craft section of Wal-Mart or the likes.  There is a two-part product that is used by florists for water in arrangements.  It is pretty cheap and comes in clear.

HeavyArty has hit on my recently found product.The one that's the cheapest & will meet your other criteria is found at The " Michaels " chain of arts & crafts in the Northeast.It's called Everlasting elegance, Manufactured in KoKamo,IN 46901 by Syndicate Sales,inc.It comes in 12 ounce bottles,I don't remember the price,just the anger In how much I was Paying for Woodland scenics scenic water.It was hugely cheaper.   Semper fi,  rudedog.I have yet to try the stuff Arty pointed out when I asked the same que, a couple months ago.But this I know from many uses.

Hmm, great ideas, but the first websites I checked had everlasting elegance listed for about 15 dollars (US) for a 12 ounce bottle, So It would end up pretty expensive for me.  I do however have a michaels craft store very close by so ill check sometime.  If i cant find a cheap source for that ill probably just see what I can do with non-clear surface, since I have seen  some very nice looking large scale waterline ship dioramas.

Found this while doing a search for Everalsting Elegance:

I used to use Everlasting Elegance....you find it in the floral department of Michael's. Much better than SW. Hardens to completely solid, doesn't bubble, and is just generally easier to use. Only drawback is the $13 a pint. So, I recently went to my auto supply store.....found a product call Everfix Epoxy (2 part) Resin (used for auto body work).....love it. It isn't perfectly clear until after it's mixed and poured. The price is much better.....I'm saving $6 a quart. And instead of waiting 7 days for it to cure completely, it only takes 24 hours......and I pour it close to an inch deep in most of my ponds. It gels in just 30 minutes.....which means that I can do a waterfall (some are almost 6" high) in less than an hour. It used to mean fussing and fussing over a single waterfall for 10 - 14 hours waiting for the resin to firm up enough to stick to well. The label even states that it is the only resin that can be poured over Styrofoam....haven't tried that yet, I'm sure that eventually I will. LOL Also has about a 10 year shelf life. The only drawback I've found with this product over Everlasting Elegance is that is does bubble more.....but the good far outweighs the bad. And while it smells, it isn't any stronger than Everlasting Elegance, and less than other resins. I use ALOT of this stuff, so I feel like I have enough experience with it to know a *really* good product when I find one. 

Wow thanks, sounds like a great project, I used 2 part epoxy resin not long ago and it was great except it yellowed too much to make very relaistic.  Ill have to try out that new stuff. The bubbling might even be a help making violent omaha water with wakes and bullets/mortars waves all that chaos.