Really depends on what you want it to do, how many things it needs to control, what you want it to monitor etc. mine is fairly basic at this stage as it only controls the temp and some lights, cost about $700 so far. It can be added to later to monitor the ph, water level, conductivity etc and activate some dosage pumps. Can even get a GSM interface to text you the levels of the tank, you can even activate diferent things on the unit that way too (great when on holiday)