Hi !
Start with a graphic adapter that worth at least 200$ or more if you can afford it, either AMD or Nvidia:
Radeon R9 280 around 230$
or
GeForce GTX 760 around 250$
or
Radeon R9 280X around 300$
Note : You can try a cheaper card (125$ to 200$) , if the rest of your rig are all top of the line. (4 ghz or more with a SSD HD)
Your game's performances will always be bottleneck by your least performing computer's component :
For the graphic card to perform at it's maximum, you need a good quad-core+ intel or AMD 3.0 mhz+ CPU as the
GPU scale with the CPU power.
You also need a good motherboard of a least 130 $ with 8 gig of good speedy memory. Try Asus
A fast main bus with a speedy memory will insure that your frame rate remain constant, meaning no frame rate drop when there is a lot of action. A powerful graphic adapter pair with a so so mainboard and memory will have high frame rate, but will also have bottleneck causing data congestion dropping the frame rate to a minimum. A add-on sound card instead of the mainboard's one will also permit a highest sound setting without creating frame drop when there is a lot of simultaneous sounds.
A SDD hard drive will make the game load a lot faster.(Optional)
It will give you a very good starting rig at around 1300 to 1500 CAD, but not the best money can buy. (1000 to 1300 USD) Or less without a SSD HD.
If your graphic adapter (GPU) has only 1 gig of memory or less, a well defrag hard drive or a SSD HD will also help for a constant frame rate as your GPU will need to swap and load textures more often from the main memory.
Important : Having the latest drivers all you computer parts will also help a lot, especially if the game is new. (less the 6 months old)
Link for GPUs performance/price :
http://www.tomshardware.com/reviews/gaming-graphics-card-review,3107-4.html
If that may help someone, i'will be happy.
See you on the battle field.