Does it have to be a food based gel/jelly? Because you can make a very clear "slime" product that may work. In case you're not familiar, making slime is an obsession with a lot of tweens around here and youtube is inundated with how to videos. Slime can be made with household products. It may work for your art exhibit as you are planning it.
Example Video
Seriously, do a search on youtube or google about making clear slime.