You should look at the stickee on this forum about how to ask for advice on video cards:http://www.tomshardware.com/forum/290969-33-advice-choosing
What online sources are you using for the purchase?
What applications and games?
What game settings?
What resolution of monitor?
What CPU and power supply does the system have?
A good place to start a search for good cards is the THG article on the best video cards for the money, updated monthly to reflect new prices and new cards. You may have to translate the prices into your currency. Also note that it includes links a very brief description of the performance level of the card plus links to reviews with detailed performance benchmarks, most often with comparisons to other cards:http://www.tomshardware.com/reviews/gaming-performance-radeon-geforce,2997.html
For more general information about how to upgrade video cards, including determining system limits and comparing, selecting and installing video cards, I recommend this site:http://www.upgradevideocards.com/index.html