2 low end cards in crossfire will perform better than 1 low end card, BUT for your $200 you could get 1 of
this or
this which would perform better and would allow for more upgrades.
There are really two main situations where crossfire is used in place of a single new card.
The first one is when you already have one fairly powerful but slightly outdated card, crossfiring with that card can boost the performance enough to hold you til a full upgrade. This will not yield as much performance as a new card, but will yield decent performance gains for the price.
The second is much less common, and that is for people who really want a lot of performance. They will simply go out and buy 2 or more of the best available, and crossfire them, simply because the performance they want isn't available on a single card. This type of setup is generally unnecessary, any single high end graphics card should be enough for most new games, and hold their own for some time.
There is little sense in buying two low end cards, especially when you can get one more powerful one for the same price. Also, when you have a single card, you can crossfire it later on when you only want to spend $100 to get some more performance.
