I would suggest going with a ati hd4850 it can be found online for $130 USD, or look at the benchmarks on the ATI HD4830($80 USD) don't know much about it but it can't be terrible. I do know however that converting to euros will be over your current 30 eur but not by a tremendous amount.
If you plan on going high end I would take a look at the nvidia cards though~ but they will cost you an arm, a leg, and a lung. Though it is worth the investment especially since you will be future proofed. Would also suggest you check if your motherboard supports the AMD64 X2 CPU's, if it does you might be best getting a cheap 2ghz+ dual core AMD cpu.
I am telling you though invest in beefy hardware, let the wife and children go hungry for a bit. When your playing demigod at 1920x1200 with maxed out graphics you will be in a true nirvana greater then sex. Ok fine I lied, sex first then the game
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I didn't notice anyone else mentioning this, so forgive me if I missed something, but the minimum processor requirement is listed as 2.4GHz for Demigod. Running it on a slower processor could definitely cause some issues.
Definately, this is the type of game where your CPU is important. As with most RTS games where tons of units each with their own AI routine need. Or games with mere programmers like Saints Row 2, where they fail to optimize code thus making CPU usage more than it should be.
Hell even on my beefy machine some CPU intensive games don't run as smooth as they should. This game does not though~ which is great even on max settings.