I am super happy you have found a game you enjoy, was worried about you for a while there!
I am sure
@MorgsGoat can point you at the best reputable PC builder (not sure on the finance stuff though), but for an example, on overclockers.co.uk there are several systems in and around the 500-650 GBP range that will suffice for some low-mid end gaming.
https://www.overclockers.co.uk/titan-kite-gaming-pc-intel-core-i3-7100-3.9ghz-fs-024-og.html#t=c3
Is an i3-7100, 8GB and upgraded to an RX 470 4GB for just over 700
https://www.overclockers.co.uk/titan-dagger-gaming-pc-intel-core-i3-i5-i7-fs-080-og.html#t=d3
i3-6100, 8GB, 1050 TI at just under 600
And for a comparison, a thoroughly middle of the pack system with an i5-7600, 16GB ram, and a 1060 6GB comes in at just over a grand:
https://www.overclockers.co.uk/ocuk...abylake-ddr4-gaming-pc-fs-19v-og.html#t=b5d1e)
Edit....the last link is refusing to include the ')' in the hyperlink, so the system is missing the 1060 card.....