depending on the +12v amperage, a 6870 is 150-160$, theres a price gap between this card and the next upgradable amd cards 6950/7850* which are 250$. the 6870 has the best price for its power. Be warned that the 6870 requires 2 6 pins
For me its going to sites like newegg and reading the responses from people who actually bought the cards and reading their experiences ..so far ..any 256 bit card can play modern games ..300+ bits card really dont have any problems playing actual games and future games ..anything under 256 ..you may have to sli it ..and im talking normal ok graphics not extreme enthusiast perfect picture/fps ...it just depends on what you want . I really dont care about maxing graphics as long as i can see what I'm killing... its ok !! lol ..