To anyone that is reading this and looking for the answer...
You can set something efficient up for approximately £65 - £150. Likely less if you have some bits and bobs laying around or you reuse an old computer to serve it. Shopping around is how you get it lower, and the higher end of the price is to note that it's more than what you would need so allows some wiggle room for active use and other uses out of the server set up. To make things a little more realistic you can set something decent up for £80 - £100. (although storage capacity will be lacking at that price, enough to get things going and upgrade later if needed)
From everything that I've found it's very situational to determine the cost. It would cost me approximately £8/yr to run it in active use rounding up and assuming most strenuous electricity usage. Although if you use a meatier set of hardware components that will ramp up the cost of running it, so unless you need more out of something, try to find an optimal middle ground or you'll be paying for more than you need in electricity bills.
Thanks for the response and if anyone else would like to add to this for others who are looking for the same information then it would be appreciated.