I'm thinking something like this:
PCPartPicker part list / Price breakdown by merchant / Benchmarks
CPU: AMD A8-6600K 3.9GHz Quad-Core Processor (€94.90 @ Caseking)
Motherboard: ASRock FM2A55M-DGS Micro ATX FM2 Motherboard (€43.00 @ Amazon Deutschland)
Memory: G.Skill Sniper Series 8GB (2 x 4GB) DDR3-2133 Memory (€70.13 @ Amazon Deutschland)
Storage: Western Digital Caviar Black 1TB 3.5" 7200RPM Internal Hard Drive (€72.90 @ Caseking)
Case: Fractal Design Core 1000 MicroATX Mini Tower Case (€37.89 @ Amazon Deutschland)
Power Supply: XFX 550W 80 PLUS Bronze Certified ATX12V / EPS12V Power Supply (€54.90 @ Caseking)
Total: €373.72
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2013-09-22 16:41 CEST+0200)
And then he can add a GPU when he has another 150 euro, or maybe ask for one for Christmas. The RAM is 2x4GB CAS10 2133MHz. He can get a copy of Windows 7 or 8 from University.
Just wondering if he should get the A10 instead of the A8, has an HD 8670D instead of 8570D and it is clocked 200MHz higher for 25 Euro. Or there is the A6-6400K dual-core with the HD 8470D iGPU and 3.9GHz clock speed for 60 Euro.