As far as I know, the active ingredient in most chemical drain cleaning products is NaOH - Sodium Hydroxide - Caustic Soda - Lye etc. I've looked at the ones in the hardware store here and the only real difference between the ones labeled "professional" and ones labeled "household" is the concentration.
Some of them may have some form of stabilizer or maybe a catalyst or some other form of "inactive" secondary ingredients that are intended to help the process along in some way.
This is similar to the products for mildew removal. They're primarily a Sodium Hypochlorite solution providing active chlorine. Some may also include a surfactant, or other secondary chemical to assist the job.
For me, I get granular Sodium Hydroxide in a 4lb container, and granular pool chlorine also in a 4lb container (the pool chlorine contains a range of other things like algicides and fungacides into the bargin). This is far cheaper in the long run and one can tweak the concentrations of the end product well but one must be careful of how they're used and the concentrations in which they're used to avoid injury or damage to what you are cleaning.