I personally use lava rock and packing peanuts in my 800 gallon system and it works very well. The lava rocks make a terrific substrate for my pothos plant to take root in as well. A large bag of packing peanuts cost me $5 off ebay and the lava rock cost $1.99 a bag from my local landscape supply, all in all I probably have $20 in media for my large system
I use 5 drawer sterilite towers to put it all in fed by a 50 gallon rubbermaid tub that is half full of laval rock and being overrun by Pothos, 0 ammonia, 0 nitrite and 5-10 nitrate in a system with over 150 messy african cichlids.