Processor - Intel Pentium G860 Sandy Bridge 3.0GHz LGA 1155 65W - $90
RAM - G.SKILL Ripjaws Series 4GB 240-Pin DDR3 SDRAM DDR3 1333 (PC3 10666) -$22
Motherboard - ASUS P8H77-V LE LGA 1155 Intel H77 HDMI SATA 6Gb/s USB 3.0 ATX - $122
Power Supply - CORSAIR Builder Series CX430 V2 (CMPSU-430CXV2) 430W ATX12V v2.3 80 PLUS - $45
CD/DVD Drive - SONY Black 18X DVD-ROM 48X CD-ROM SATA DVD-ROM Drive Model DDU1681S-0B - $17
Case - Rosewill BLACKHAWK Gaming ATX Mid Tower - $90
Pick your hard drive, however much you need. 1TB goes for $90.
You'll be getting a 550 Ti from Zack for your graphics card.
A copy of Windows 7 32 bit is $120 or so (you can find cheaper probably).
A monitor/keyboard/mouse is about $200 for a nice one.
So in total, $796 or 649 euros, for everything. If you already have a monitor or a copy of Windows 7, that's ~$300 off.
This'll run AH on high settings (not completely maxed, but high) with 60 fps. You'll pull off maybe 40-50 fps in RoF with mix of medium/high settings. Microsoft Flight Sim X will be maxed, DCS: A10 and P51D will be mix of medium and high most likely.