Whilst the PC itself is a large contributor, it also relies a lot on the graphics card. I mean I wouldn't know your budget, but there is certainly some good graphics cards out there which aren't ridiculously expensive, for example GTX 1060, (which is like £300), the next addition up from this is the 4k HD one which is a lot of money. The GTX 960 is quite nice too, if you're lucky you might be able to get your hands on one for like £100.
(Hope this was helpful).