Newark sells some cheap RH sensors made by honeywell. They are based on humicap technology (much better than hygristors). They work well in the lab, but have a significant light sensitivity. We tried them in the field on some weather towers, but could not shield them from the sun well enough so we went back to viasala sensors at 10x the cost. As long as you know about the light problem and don't mount them under a halide or in the sun they will work well.
For a cheap AC voltage sensor we use an unregulated DC adaptor. The output is linear with input AC voltage.
To get Watts you will need to know the power factor or measure the phase difference between the current and the voltage. Analog devices makes a cheap chip that can do this, but I have not tried it. Or you could program in a constant as an approx. Most of my equip has a PF of .95, but the power heads have a PF of .50. For my power heads 1A * 120 V = 60 watts.
Since the controller will know what equipment is on, if it measures current and the reading is different than expected that could indicate a malfunction.
If you want some help I would be interested, not that I think you need any help.
