Electricity and heat is no issue for me as electricity is included in the rent of my office, and we currently use electric heaters to keep the office warm...
Also: a 2 year old server can be bought for about 1k, you can't get the core count and amount of RAM new for that price.
My entire tech power load, which includes my APC UPS, ubiquiti router and access point, 8 port gigabit switch, MoCA bridge, the above mentioned Dell server, and a Mac mini for remote Mac development, consumes about 100w at a steady state as measured at the outlet with a kill-a-watt meter.
At my current utility rates that comes out to be about $8.62 a month - not free but certainly imo a good investment to have local VPN, data storage, ESX and KVM virtual machine hosting.
But if you skip forward a few years, a 2012-2013 quad socket, eight core Xeon machine that was many thousands of dollars is still quite useful. If you want to lab your own xen or kvm hypervisor stuff on a machine with 32 cores and 256GB of RAM you can do it for under $1000, if you know where to look, and can tolerate a 500W load addition to your electrical bill.