If its gaming PC then you need to decide the level of Graphics card you want to pay for .. nowadays most mid level cards can cope with the majority of games.
The GFX card really should be the most expensive single part in a
gaming PC
A couple of years ago I went to a 2nd hand top end card of a previous year, A GTX 295) original RRP £500+)
got it for £90 and its only now just starting to show its limits @ 4 years old.
C.