But we lack the budget. I agree that moving to the newest platform is the better idea, but if the budget doesn't allow it then it doesn't allow it. Option one is cheapest, just buy a new 8320 for 150 euros. Option 2 is next cheapest where you buy a new Intel CPU for 150 euros, and a board that will run it for 60-75? He can reuse the DDR3 memory he's got now, and it's only ~200+ total. (225? Again, don't know what the budget allows.) Option 3 is the most expensive but of course provides the biggest boost. New skylake build with DDR4. Don't get me wrong, would be "best". But it's also the most expensive and might be out of reach.
Looking on that website I do see the i3 6100 is around 120. That's a good entry gaming CPU. You...