On the cheap side for substrate, I did the following:
-Substrate Upper Layer (1")
Mostly gravel (1-2mm, actually pool filter media)
-Substrate Lower Layer (2")
50% Schultz/Profile Aquatic Potting Soil (similar to laterite)
25% gravel (1-2mm, actually pool filter media)
25% sand.
The Aquatic Potting Soil is not QUITE as good as actual laterite I've been told, but it was cheaper here. I hear from LFS there is a newer product (imported from Germany?), can't remember the name, which is a very small, reddish granule (<1mm size) that is a very good substrate/additive and will also maintain a slightly lower pH if that's what you're looking for.
