Totally man! With todays technology stuff like this can be achieved pretty easily. The main thing you will want to spend your money on is the Graphics Card, I am using a 770 and Arma 3 runs at 30+ on ultra, tune down the setting a little bit and you will be golden. Don't worry too much about most other parts. 8gb of ram is the sweet-spot and an SSD would be nice if you really don't like loading times with Arma. Look in my signature for my build, cost around $1000 without OS.
Hope this helped!
~Sevenater