Is he comfortable adding the FSR mod?
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If so looks like a 1660 super level would be more than sufficient with FSR. That costs around £350 in the current GPU shortage based on OCUK prices. Maybe double check if you don't go AMD that FSR will work on the card you choose. So for a whole machine in the range of £750ish - £850ish.
I would be inclined to wait 12 months and see if prices come crashing down on GPUs.