Given the cost, the ADA AS substrate is much cheaper than 30$ a bag!
You need two bags to = one 9 liter ADA AS bag.
ADG has it for around 26$ a 9 liter bag which is good for about a 20 gal.
You can also pour it directly into the tank without rinsing it, EC is wet and you pay for water in the volume and the weight.
And ADA is better than the other's mentioned here.
I've used kitty litter in the past with great success, but it's messy when you do large reworks and uprooting.
Tropica has come out with a new clay semi soft substrate as well, but it's not here in the USA yet, AGD will likely be carrying it soon though.
I've used all the metnioed substrates, I fully suggest the ADA substrate, the medium size amazonia.
Looks nice and it is fairly easy to work with and unlike the other hard subs, this will never scratch your glass when you clean or scrub the glass.