https://uk.pcpartpicker.com/list/VpymVw
good build in your budget range (you should learn how to build a computer its not hard, theres youtube videos that show you literally step by step what to do, what order, what screwdriver etc)
I don't know many good prebuilt pc websites apart from overclockers, but thats UK only I believe. Would be worth researching and finding something similar to the build I sent.