prices for used graphics cards are grossly inflated here, but you can get a 560 in good condition for 40€ and last month i saw 570s for 50€ etc.
dont expect to find that perfect deal right away, patience is a virtue.
stay away from the gtx 650, i have one and it's a total turd. get the 650TI if possible, or as stated before a 560/570.