Craigslist may be a great way to start, our even local(non chain) fish stores. And what I do when I dirt a tank I start with some red clay(go to the craft store its not that expensive, and its much much cheaper then laterite which you can get at a
lfs) red and terra cotta work the same, both contain a lot of iron. Next you need ORGANIC soil. "Miracle Grow" makes one thay works great. when you put it all in pour in water slowly so that the soil will absorbe the water(you will see it puddle and then disappear). When you have it all wet add some pea gravel or whatever gravel you would like to cap(just make sure there are no chemicals) if you want dwarf cichlids peat gravel wouldnt be a bad choice either(peat will soften the water, and it may tinge the water yellow a bit, but thats not bad either). Next you pour in your sand at the level you want. I recomend wasing your sand out a bit. It will remove a lot of impuraties and then finer "non sinking" particles. Next add in news paper "crumpeled" and get the news paper wet.....with a spray bottle if you have one....then you can add in water. This will keep the sand and soild from completly mixing and spreading throughout your tank. Good idea is to add in decor you want like rocks or driftwood. You can always add in your plants later, but at this point you are ready to go when you get them. If you go to Lowes for all of this, the bag of dirt is about $8 (42lb bag....you don't need that much), leveling sand is $3/$4 a bag, you would need maybe 3/4 a bag of sand....maybe....and gravel will vary...stone yards may be your cheapest bet as will if you want to save money for better things.....like plants....or fish