Transparency really does limit your choices and make it more difficult.  And if it's see-through, you'll see the armature inside. 
When I picture a jellyfish, I see a bell-shaped body that partly opens and closes like an umbrella to swim, and lots of trailing wobbly bits and long tentacles - maximum degree of difficulty!  Maybe yours is like a shapeless blob sliding along the ground?
Liquid latex does dry a bit translucent - I use if for things like bat's wings.  But it is for making a thin skin, not a thick solid cast.  It needs to air dry. 
The professional way would be to sculpt, make a mould, then cast in a silicone rubber like Platsil Gel-10 or Dragon Skin.  But that is complex and expensive.
Clear caulking silicone - the stuff that comes in a tube to put in a caulking gun thing -  might be a cheaper alternative, and could be done by building up over armature wire.  It's not an easy material to model but can form some interesting blobby shapes.  Probably a clear one made for use in bathrooms or to seal fish tanks.  Some pieces can be cast in moulds if you need good surface details, then stuck on - as long as the mould is open on one side to let air in.  If it's too sealed in it takes a very long time to cure.