is there a cheap alternative to dried flower arranging?

The "floral setting resin" that's used for putting silk flower stems, etc, into inside a container is pretty safe, especially when compared to the other types of resin.

You can read about that type of resin on this page at my site if you want more info about it:

http://glassattic.com/polymer/other_materials.htm

....click on the category called SOFTER-SURFACE EPOXY RESINS

Nothing will end up quite as clear as a resin though when it's used that thick, but if you could get away with not-too-much liquid (especially in a smaller container), you could also use a (water-based) gloss polyurethane, or perhaps even a cheap cyanoacrylate floor polish like Future/Pledge or Mop'N Glo the same way. Clear acrylic mediums (sold for acrylic paints) would work too but won't be as cheap as those.

There are also some meltable crystal gels that cure clear but not sure how expensive they'd be or how "safe" they are.

You could always use mechanical things to hold the stems in place, like glass pebbles, small rocks, or aquarium gravel, etc, though those wouldn't simulate water (unless they were blue?). Or you could use an air-dry clay like salt dough clay perhaps, then cover it with something blue or something one would find under water.

Or you could use wads of plastic wrap, perhaps set with some of the polyurethane or cyanoacrylate mentioned above.

HTH,

Diane B.

if it's for children, i'd suggest play-doh or blue tack type things

:-)