One way is to buy low w parts or nucs but often they have either high input costs at the start or older hardware has low horsepower or limitations like nucs having 8 gig ram limitations. What ways do members here reduce powerbill
Most NUCs come with 2x SODIMM slots which can be loaded with 16gb sticks giving you the option to install 32gb of ram and older hardware will indeed have power consumption issues.
You should do calculations based on the electricity rates in your area. At most it'll be 500-1000 INR/month if you are running multiple NUCs at maxed out loads.
I run 2x 65W machines(1 laptop, 1 mini pc), switches, router, APs, rpis, lte modems and all of it consumes close to ~200W at peak and my electricity bills have increased probably by about 3-500 INR/mo
(electricity cost here is 7 INR/kw)
My home server is a i3 10100 with 32GB, 1 ssd and 1 spin drive.
The average power draw is between 35-40W that translates to about 1 unit a day (24x0.04)
However, the server needs a ups for obvious reasons even though power failures are rare.
That adds another 14-15W extra.
But even that 50-55W is a relatively small add to the overall dead load of a typical household so don’t worry about it too much.
Depends on the purpose of the home lab. If the primary purpose is just to act as NAS, then something like Raspberry Pi or Synology works well with very little power draw. If you want to host a plex server, which needs slightly more processing power, Intel 8th and 9th gen NUCs, with i5 processors should be more than capable. These have a power draw of about ~65 watts max, if I'm not mistaken. To this you'll have to add the power draw of externa HDDs, router (which is very little tbh), and UPS.
Mostly, if you are concerned about power consumption, then mobile processors are the way to go. They are far more efficient. Devices like Intel NUC are also very compact and a good fit for home labs.
Depending on usage, one can also consider if everything needs to keep running 24x7. For instance, I have scheduled my Synology NAS to shutdown from 1 AM to 6 AM since I never use it during that time and it can power own automatically. I also have an Amazon Plug which powers off my TV, AVR, and Raspberry Pi (which runs LibreELEC) at 12 midnight and powers it on at 8 AM. Standby power consumption for these devices are anyway pretty low, but I still prefer having them powered off at night.