Just recently, I finished the first part of a three part article on vivaria substrates for amphibians. I'm not sure if you have seen it yet, but while written with newts and salamanders in mind, it is very useful for frogs and toads. (the second part covering terrestrial substrates will be finished shortly and available to read soon!)

Have a look at it, as it covers the reasoning behind dumping gravel for sand, and low cost alternatives to those very pricey off the shelf products. The references are very useful to frog folks also, and many of them are readily available online to read.