It's not the CPU that's power hungry. It's everything.
That Xeon is around 2x as powerful as the G1610T in the MicroServer Gen8, so given you have 2 of them, around 4x as powerful overall. But probably around 10x the power consumption, which isn't cheap in the UK. At 11p per kWh (what I pay for my electricity), 200W is £0.53 per DAY, or £193 per year. 200W adds up quick when it's running 24x7.
The £20 is worth paying just for the experience of playing with and setting up a proper server. But definitely not worth running 24x7.