there are several that are made equally, basically take your pick, To use a plc is good, you can buy them cheaply. the best way to save money is to have the unit powered through a variable Frequency drive(VFD) it controls the hertz and can slow down or speed up a compressor depending on load. Its a great way to save on electrical cost. If you turn it on and the RH is high, it will go full speed, but as you approach the desired set point, rather than cycling, it will slow down the compressor. This accomplishes two things 1: etremly tight control of rh, and gets rid of voltage spikes from lock rotor amps at start. Allen Bradley makes very reliable ones, and they are easy to set up