If your electricity bill is growing too high all you have to do is reduce your energy consumption, fell two or three GPU and keep mining with the rest or if you have some money then build a solar energy instead, this is what I use
Major problem is 'over-clocking', I run my gpus at about 60watts, so my power consumption is minimal, I want the temp of gpus less than 70C so they don't die.
By default the cards are running 150 watts, but that additional power is 10% boost, I would seriously step back and quit wasting your money
Most of the stuff about GPU mining is BS, noobs always focus on 'over-clocking', which kills their cards these days you can't buy new cards, we take care of our cards,
Dropping the power as low as you can right there would save you 75% of your current cost, 50% would be easy.
Learn, just do the 'nvidia-smi -pl N -i M' and where M is the gpu card, and N is the power in watts, and keep dropping until the MH rate goes to zero, then start rising again to find the sweet spot. You will fine that that you can mine at -60% of default power, and still get 90% of the MH rate
Lets see your 18 cards at 150 watts = 2700 watts, where I live that would be $1500/month, I pay $120/mon because I reduce power. I try to run the total under 800Watts