So the max money I'm able to spent are ~500-700 Euros (for a gpu).
What should i bee looking into when I'm also interested in mining?
7970 is the top gpu miner, and a very good card for gaming too. You can buy two with that budget which should be 1ghash+.
If you have the money thats a great card. Don't forget a great power supply and you might want to open up your case to help with the heat.
Mining gets these cards hot.
so good power supply (especially if you are running more then one card)
and alot of fans ... double the amount you think you need. Its summer in the USA if that is where you are then you cannot run enough fans .
think small airplane engine.
you can always remove some in the winter if you are still mining by then.