If you want to save money on media... put each plant in a pot.
It doesnt have to be a big pot. you can take a 4" rockwool cube, put it in a pot surrounded by hydroton, and flood accordingly (maybe once per day, more if it's a smaller rockwool cube and there is more hydroton pebbles)
pots also help in moving plants around for better lighting circumstances. ie: bigger plants on one side, smaller on the other, so you can lower one side of your light.
cheapo plastic pots are about a dollar each, made of plastic, and you can reuse them many many many times. they have holes in the bottom and the water enters the pot through those holes.
Just a suggestion.
oh, and airstones are not necessary, I run ebb and flow and I dont use airstones. The process of the plants drying out over time provides them with oxygen. To me, airstones are just another thing to clean, and an airpump is just another thing to plug in. simplifyyyyyyyyyy is my motto!
Oh, one more thing with the pots, if you choose to use them, it doesnt matter if your tray is clear. I also use one of those 'under the bed' storage containers that I got from Target, I dont bother with painting it or anything, because the roots stay in the pots and are never exposed to light. Easy Peasy.