If you want cheap and will grow almost anything grab the cheapest potting soil you can find, ie. no additives and top it with sand or gravel to prevent it from cloudy up the water. It might do some weird things in the first couple of weeks, but it comes down in a month or so, pretty much the poor mans' ADA amazonia soil.
that sounds like something i would do.. it doesnt break up and float all over the water column?
where do you find that???? Please tell me lowes!!???