bf3 isn't that good i would suggest arma 2 
Random comment that answers no one's question.
And no problem Ace, happy to answer any questions.
And yes, those high end cards are expensive for sure, but if you have the muula now, it's worth it, because those card will run every game today, and possibly every game 2 or even 3 years into the future. Much better than buying a new mid range card every year.
Of course, if you're ok with medium or playing on a lower resolution, then go for a cheaper card.
Radeon 5770 is still a very good card, 4850 is rather old but still run today's games decently, 6850/70 like Jäger said is also good.
I myself run a 5570, which is extremely cheap for it's performance and power consumption. Only $70 on Newegg. It runs the newer games fine on lower resolutions or lower settings fine. (I can run Skyrim, BF3, Shogun 2) all on medium/high settings at 1920x1080. Only Shogun 2 lags for me at times, but I can always drop the resolution down further.