I agree with kobus, hydroton can be expensive, but only if you need a lot of it. I wanted to try expanded shale, but no where to buy it the PNW that I have found, and shipping it here is twice as much as the bag costs.
I have an indoor system that has been using lava rock - which is WONDERFUL and my tank has been maturing with it in the filters, not one issue. The lava rock is sharp however. The way my tank is set up I rarely have to get in the filters, they are all permanent plantings. I'm starting a grow tower to drain into my tank soon, however, and am picking up a bag of hydroton for ease of digging the crops I want to plant.
You can use "Turface" It's about 13 bucks for a 50lb bag. Gotta rinse it thoroughly. Most irrigation supply stores have it.